RF Energy Delivery System and Method

ABSTRACT

A radio frequency tissue ablation system with a radio frequency generator, the generator comprising a radio frequency source, at least four independently controllable radio frequency outputs, a user interface and a controller configured to delivery radio frequency energy from the radio frequency source to the radio frequency outputs in one of at least two different output configurations in response to a configuration selection made through the user.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/928,788, filed May 11, 2007, which application is incorporated byreference as if fully set forth herein.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to ablation systems and methodsfor performing targeted tissue ablation in a patient. In particular, thepresent invention provides radiofrequency (RF) energy generators thatcreate safe, precision lesions in tissue such as cardiac tissue.

Tissue ablation is used in numerous medical procedures to treat apatient. Ablation can be performed to remove or denature undesiredtissue such as cancer cells. Ablation procedures may also involve themodification of the tissue without removal, such as to stop electricalpropagation through the tissue in patients with an arrhythmia condition.Often the ablation is performed by passing energy, such as electricalenergy, through one or more electrodes and causing the tissue in contactwith the electrodes to heat up to an ablative temperature. Ablationprocedures can be performed on patients with atrial fibrillation byablating tissue in the heart.

Mammalian organ function typically occurs through the transmission ofelectrical impulses from one tissue to another. A disturbance of suchelectrical transmission may lead to organ malfunction. One particulararea where electrical impulse transmission is critical for proper organfunction is in the heart. Normal sinus rhythm of the heart begins withthe sinus node generating an electrical impulse that is propagateduniformly across the right and left atria to the atrioventricular node.Atrial contraction leads to the pumping of blood into the ventricles ina manner synchronous with the pulse.

Atrial fibrillation refers to a type of cardiac arrhythmia where thereis disorganized electrical conduction in the atria causing rapiduncoordinated contractions that result in ineffective pumping of bloodinto the ventricle and a lack of synchrony. During atrial fibrillation,the atrioventricular node receives electrical impulses from numerouslocations throughout the atria instead of only from the sinus node. Thisoverwhelms the atrioventricular node into producing an irregular andrapid heartbeat. As a result, blood pools in the atria that increases arisk for blood clot formation. The major risk factors for atrialfibrillation include age, coronary artery disease, rheumatic heartdisease, hypertension, diabetes, and thyrotoxicosis. Atrial fibrillationaffects 7% of the population over age 65.

Atrial fibrillation treatment options are limited. Lifestyle change onlyassists individuals with lifestyle related atrial fibrillation.Medication therapy assists only in the management of atrial fibrillationsymptoms, may present side effects more dangerous than atrialfibrillation, and fail to cure atrial fibrillation. Electricalcardioversion attempts to restore sinus rhythm but has a high recurrencerate. In addition, if there is a blood clot in the atria, cardioversionmay cause the clot to leave the heart and travel to the brain or to someother part of the body, which may lead to stroke. What are needed arenew methods for treating atrial fibrillation and other conditionsinvolving disorganized electrical conduction.

Various ablation techniques have been proposed to treat atrialfibrillation, including the Cox-Maze procedure, linear ablation ofvarious regions of the atrium, and circumferential ablation of pulmonaryvein ostia. The Cox-Maze procedure and linear ablation procedures aretedious and time-consuming, taking several hours to accomplish.Pulmonary vein ostial ablation is proving to be difficult to do, and haslead to rapid stenosis and potential occlusion of the pulmonary veins.All ablation procedures involve the risk of inadvertently damaginguntargeted tissue, such as the esophagus while ablating tissue in theleft atrium of the heart. There is therefore a need for improved atrialablation products and techniques that create efficacious lesions in asafe manner.

SUMMARY OF THE INVENTION

Several unique radiofrequency (RF) energy generators and ablationcatheter systems and methods are provided which map and ablate largesurface areas within the heart chambers of a patient, with one or fewcatheter placements. Any electrocardiogram signal site (e.g. a site withaberrant signals) or combination of multiple sites that are discoveredwith this placement may be ablated. In alternative embodiments, the RFgenerators and/or ablation catheters may be used to treat non-cardiacpatient tissue, such as tumor tissue.

Advantages of the invention may include one or more of the following.The system and method provide maximum flexibility, efficacy and safety.The system and method provide independent delivery of monopolar and/orbipolar RF energy to multiple (e.g. 4, 8 or 12) user selectableelectrodes. Monopolar energy delivery provides lesion depth and bipolarenergy delivery provides lesion fill between selected electrodes.Sequential and/or simultaneous delivery of monopolar and bipolar RFenergy can provide variable-depth linear lesions with a single or areduced number of applications of energy. The system and method providesafe, precisely controlled delivery of RF energy to tissue.

In one embodiment, a constant voltage source is utilized for all pairsof RF outputs (channels) and adjustment of the phase angle of theapplied (RF) voltage produces different ratios of simultaneous and/orcumulative monopolar and bipolar energy delivered such as to createvaried length and depth lesions in the tissue of a patient.

In another embodiment, a varied voltage source is utilized for all pairsof RF outputs and adjustment of the voltage amplitude or other appliedvoltage property produces different ratios of simultaneous and/orcumulative monopolar and bipolar energy delivered such as to createvaried length and depth lesions in the tissue of a patient. In thisembodiment, the duty cycle used during energy delivery may be fixed, oralternatively it may be varied such as a configuration in which aminimal duty cycle is used which incrementally increases to reach atarget tissue temperature. In this embodiment, the phase shift may befixed, such as fixed at 90° or 180° phase shift to create the bipolarenergy. The RF generator of this embodiment includes variable powersupply circuits for each RF output.

In yet another embodiment, varying the average “on” time of bipolarand/or monopolar power delivery is utilized for all pairs of RF outputsand adjustment of this average produces different ratios of simultaneousand/or cumulative monopolar and bipolar energy delivered such as tocreate varied length and depth lesions in the tissue of a patient. Theratio of bipolar fields (or combined monopolar-bipolar fields) tomonopolar fields may be adjusted to achieve a desired power level and/orbipolar-monopolar ratio. Alternatively or additionally, the duty cycleratio within the bipolar fields (or combined monopolar-bipolar fields)and the monopolar fields may be adjusted to achieve the desired powerlevel and/or bipolar-monopolar ratio. Alternatively or additionally, thefields length of the bipolar fields (or combined monopolar-bipolarfields) and the monopolar fields may be adjusted to achieve the desiredpower level and/or bipolar-monopolar ratio.

The RF generators of the present invention may employ one or more energydelivery algorithms to control power delivery. In one embodiment, analgorithm provides energy at a fixed power, such as a maximum power,until the tissue to be ablated reaches a first temperature level. Fortemperatures above the first temperature level, power is delivered at alevel determined by the actual tissue temperature. Target temperaturelevels and/or threshold temperatures may be adjustable by an operator ofthe system. In another embodiment, an algorithm employs a main controlloop based on a power differential analysis and a secondary control loopbased on a temperature differential analysis.

The RF generators of the present invention may employ a multiplexingmodule which allows an operator of the system to selectively pair RFoutputs from a group of three or more RF outputs to deliver bipolarenergy between the selected pair.

In another embodiment, the system and method include closed loop energydelivery for each RF output including a PID control loop which receivesinformation from a thermocouple mounted proximate each electrode on theablation catheter such as to provide closed loop energy delivery basedon measured tissue temperature. Power delivery may be duty cyclecontrolled to improve lesion creation efficiency, providing low powerablations. Duty cycle control allows delivery of high peak powers whileproviding electrode cooling times during the off cycle. In addition,duty cycle power control simplifies design and control of multiple RFoutputs utilizing different phase angles. Duty cycle energy deliveryalso improves temperature acquisition as data can be acquired during theoff portion of the duty cycle (i.e., during the RF “quiet time”). Thesystem and method including temperature acquisition provide fast,accurate and electrically-isolated temperature acquisition for allelectrodes. Each catheter electrode may include a small massthermocouple. The system and method provide safe, controlled energydelivery.

In yet another embodiment, the RF generator includes a first set ofablation parameters that are utilized when a first form of ablationcatheter is attached to the RF outputs and a second set of ablationparameters that are utilized when a second form of ablation catheter isattached to the RF outputs.

In yet another embodiment, the RF generator includes an improved EKGinterface for connecting the RF outputs to an EKG diagnostic device.When one or more ablation catheters are attached to the RF generator,the electrodes of the ablation catheter are electrically attached to theRF outputs of the RF generator. The improved EKG interface of thepresent invention attenuates the energy delivered to ablate tissue to alevel to prevent damage to any attached EKG diagnostic device, yetallows EKG or other signals sensed by the electrodes to be transferredto the EKG diagnostic device with minimal attenuation of those signals.

According to another aspect of the invention, a system for performing anablation procedure is described. In one embodiment, one or more ablationcatheters are provided with an RF generator of the present invention. Inanother embodiment, a remote control is provided with the RF generatorof the present invention.

One aspect of the invention provides a radio frequency tissue ablationsystem including a radio frequency generator. The generator has a radiofrequency source, at least four independently controllable radiofrequency outputs, a user interface and a controller configured todelivery radio frequency energy from the radio frequency source to theradio frequency outputs in one of at least two different outputconfigurations in response to a configuration selection made through theuser interface. In some embodiments, the controller is furtherconfigured to operate each output in either a monopolar mode or in abipolar mode or possibly in a combination monopolar/bipolar mode,possibly in response to a configuration selection made through a userinterface. The system may also include a ground pad connected to aground source when the outputs are operated in both monopolar mode andbipolar mode.

In some embodiments, the controller is further configured to deliverradio frequency energy from the radio frequency source to the radiofrequency outputs in a plurality of successive time fields each having aperiod. The time fields may have a duty cycle with a portion of theperiod when radio frequency energy is being delivered to the outputs andanother portion of the period when radio frequency energy is not beingdelivered to the outputs. The controller may be further configured toadjust the duty cycle in response to a configuration selection madethrough the user interface. In some embodiments, at least one time fieldof the plurality of the successive time fields is monopolar for at leasta portion of the period, and at least another time field of thesuccessive time fields is bipolar for at least a portion of the period.In such embodiments, the controller may be configured to adjust a ratioof bipolar to monopolar time fields in response to a configurationselection made through the user interface. One time field may be acombination monopolar/bipolar time field. The controller may also befurther configured to adjust a length of at least one time field inresponse to a configuration selection made through the user interface.

In some embodiments, the radio frequency source is a constant voltagesource, and in some embodiments the radio frequency source is a variablevoltage source, in which case the controller may be further configuredto vary voltage amplitude in response to a configuration selection madethrough the user interface. In some embodiments the controller isfurther configured to adjust voltage phase angle of the RF source,possibly in response to a configuration selection made through the userinterface. In some embodiments, the controller includes a time divisionmultiplexor.

In some embodiments, the radio frequency generator further includes anelectrode tool interface configured to detect an identifier of a radiofrequency electrode tool connected to the interface, the controllerbeing configured to adjust radio frequency energy delivery parameters toan radio frequency electrode tool based on the identifier detected bythe interface. Such systems may also include a first radio frequencyelectrode tool having a first electrode configuration and second radiofrequency electrode tool having a second electrode configurationdifferent from the first electrode configuration, the first and secondradio frequency electrode tools each having a connector adapted toconnect to the radio frequency generator electrode tool interface, theconnector of each tool having a unique identifier adapted to communicatewith the radio frequency generator electrode tool interface.

Some embodiments according to this aspect of the invention have a groundpad, with the controller being configured to connect and disconnect theground pad to a ground source in response to a configuration selectionmade through the user interface. In some embodiments, each output has anoutput line, a return line and a resistance between output line and thereturn line. The resistance may have a value that provides signalstability on the output during light load conditions at the output.

Another aspect of the invention provides a radio frequency ablationsystem having a radio frequency generator; a plurality of radiofrequency electrodes; a temperature sensor; and a controllercommunicating with the temperature sensor to control an amount of energydelivered to the electrodes in a first portion of an energy deliverysession irrespective of temperature sensed by the temperature sensor andin a second portion of the energy delivery session based on thetemperature sensed by the temperature sensor. In some embodiments, thecontroller is configured to cease energy delivery to the electrodes whena predetermined target temperature is sensed by the temperature sensor.The system may also have a user interface adapted to set the targettemperature.

In some embodiments, the controller is further configured to cease thefirst portion of the energy delivery session when the temperature sensorreaches a threshold temperature that is a predetermined amount lowerthan the target temperature. In some embodiments, the controller isconfigured to cease the first portion of the energy delivery sessionwhen temperature sensed by the temperature sensor reaches a thresholdtemperature. The system may also have a user interface adapted to setthe threshold temperature.

In some embodiments, the controller is configured to independentlycontrol energy delivery to each electrode. The system may also have atemperature sensor associated with each electrode, with the controllerindependently communicating with each temperature sensor in thedelivering step to control the amount of energy delivered to theelectrodes. In some embodiments, the controller is configured toindependently control energy to a pair of electrodes and at least oneother electrode.

In some embodiments, the controller is configured to deliver radiofrequency energy in a plurality of successive time fields each having aperiod and a duty cycle comprising a portion of the period when radiofrequency energy is being delivered to the electrodes and anotherportion of the period when radio frequency energy is not being deliveredto the electrodes. The controller may also be further configured toadjust the duty cycle based on monitored temperature.

Yet another aspect of the invention provides a radio frequency energygeneration system for delivering radio frequency energy to a cardiacablation catheter. In some embodiments, the system has a radio frequencygenerator adapted to deliver radio frequency energy in both monopolarand bipolar modes to an ablation catheter, wherein the ablation catheterhas an electrode array comprising at least one electrode; an EKGmonitoring unit adapted to monitor and map signals detected by theplurality of ablation catheters; and an interface unit including aninductor which couples the radio frequency generator and EKG monitoringunit to filter radio frequency signals from EKG signals received by theEKG monitoring unit.

In some embodiments, the at least one electrode is adapted to monitorthe temperature of atrial tissue adjacent the electrode, and thegenerator generates radio frequency energy based on the temperature ofthe atrial tissue. There may be a plurality of electrodes, and thegenerator may be adapted to independently monitor the temperature ofatrial tissue measured by each of the plurality of electrodes, and theradio frequency generator may be adapted to generate and deliver radiofrequency energy to each of the plurality of electrodes based on theindependently monitored temperatures.

In some embodiments, the EKG monitoring unit has a plurality of inputsand an inductor associated with each input. In some embodiments, thegenerator is adapted to deliver energy in a bipolar mode, a monopolarmode, and a combination of both bipolar and monopolar, such as inbipolar to monopolar ratios of at least 4:1, 2:1, and 1:1.

Still another aspect of the invention provides a method of deliveringradio frequency ablation energy to a patient's tissue, such as hearttissue, prostate tissue, brain tissue, gall bladder tissue, uterinetissue, or tumor tissue. The method includes the steps of deliveringradio frequency energy to a plurality of electrodes to heat thepatient's tissue in first and second portions of an energy deliverysession; monitoring temperature of the patient's tissue during thedelivering step; delivering radio frequency energy at a power level inthe first portion of the energy delivery session, the power level beingirrespective of monitored tissue temperature; and controlling radiofrequency energy delivered to the electrodes in the second portion ofthe energy delivery session based on monitored tissue temperature.

In some embodiments, the method includes the step of ceasing energydelivery when a predetermined target tissue temperature is reached. Themethod may also include the step of setting the target tissuetemperature. In some embodiments, the method includes the step ofceasing the first portion of the energy delivery session when monitoredtissue temperature reaches a threshold tissue temperature that is apredetermined amount lower than the target tissue temperature.

In some embodiments, the first portion of the energy delivery sessionceases when a threshold tissue temperature is reached. The method mayalso include the step of setting the threshold tissue temperature. Insome embodiments, at least one of the controlling steps includes thestep of independently controlling energy delivery to each electrode orto a pair of electrodes and to at least one other electrode.

In some embodiments, the delivering step includes the step of deliveringradio frequency energy in a plurality of successive time fields eachhaving a period and a duty cycle, where the duty cycle has a portion ofthe period when radio frequency energy is being delivered to theelectrodes and another portion of the period when radio frequency energyis not being delivered to the electrodes. In some embodiments, at leastone of the controlling steps includes the step of adjusting the dutycycle.

In some embodiments, the step of controlling radio frequency energydelivered to the electrodes in the second portion of the energy deliverysession includes the step of comparing a monitored temperature to atarget temperature and adjusting a power goal. The delivering step mayalso include the step of comparing the power goal to a power limit andresetting the power goal to the power limit if the power goal exceedsthe power limit.

In various embodiments of the invention, a radiofrequency generator fordelivering energy to ablate tissue of a patient has at least four, atleast eight, at least twelve or at least sixteen independent RF outputsconfigured to provide energy to four or more electrodes of an ablationcatheter. In various embodiments of the generator, independent RFoutputs can deliver at least monopolar, bipolar, and combinationbipolar/monopolar energy.

Another embodiment of the invention is a radiofrequency generator fordelivering energy to ablate tissue of a patient having a power scheme,including an algorithm, which initially delivers energy to a maximumpower level until the tissue reaches a first temperature, andsubsequently delivers temperature regulated power until the tissuereaches a second temperature.

Another embodiment of the invention is a radiofrequency generator fordelivering energy to ablate tissue of a patient; the invention having apower scheme, including an algorithm, which delivers bipolar andmonopolar and combination power to multiple RF outputs and which adjuststhe bipolar to monopolar ratio by varying phase angle.

Another embodiment of the invention is a radiofrequency generator fordelivering energy to ablate tissue of a patient having a power scheme,including an algorithm, which delivers bipolar and monopolar andcombination power to multiple RF outputs and which adjusts the bipolarto monopolar ratio by varying the voltage source.

Another embodiment of the invention is a radiofrequency generator fordelivering energy to ablate tissue of a patient has a power scheme,including an algorithm, which delivers bipolar and monopolar andcombination power to multiple RF outputs and which delivers the bipolarand monopolar power in sets of multiple repeating fields and adjusts thebipolar to monopolar ratio by varying the average “on” time of thebipolar and/or monopolar power delivery within each of said sets ofmultiple repeating fields.

Another embodiment of the invention is a radiofrequency generator, fordelivering energy to ablate tissue of a patient, having a power scheme,including an algorithm, which delivers power to multiple RF outputs witha first duty cycle percentage, and increases the duty cycle percentageto achieve a target temperature such as to maximize the off-time portionof the duty cycle

Another embodiment of the invention is a radiofrequency generator, fordelivering energy to ablate tissue of a patient, having multiple RFoutputs which are configured to be selectively paired to deliver bipolarenergy between the selected pair.

Another embodiment is a radiofrequency generator, for delivering energyto ablate tissue of a patient, having at least four independenttemperature inputs which are configured to receive temperatureinformation and produce four corresponding temperature signals, and atleast four PID loops configured to receive the four temperature signalsand regulate RF power delivery.

Another embodiment is a radiofrequency generator for delivering energyto ablate tissue of a patient, having a first set of ablation parametersconfigured to be utilized when a first ablation catheter is attached,and a second set of ablation parameters configured to be utilized when asecond ablation catheter is attached.

Another embodiment is a radiofrequency generator for delivering energyto ablate tissue of a patient, having an EKG interface module configuredto isolate an EKG monitoring unit from delivered RF energy whileminimizing attenuation of EKG signals received from the electrodes ofthe ablation catheter.

In further embodiments of the invention, the power scheme may initiallydeliver energy at a maximum power level until the tissue reaches a firsttemperature and subsequently delivers temperature regulated power untilthe tissue reaches a second temperature. The first temperature may beset by an operator of the system, or may be automatically set to atemperature approximately 5° less than the second temperature. Inanother embodiment, the second temperature of the radiofrequencygenerator is set by an operator of the system. In another embodiment,both the first and second temperatures are set by an operator of thesystem. In yet another embodiment, the first temperature isautomatically set to a temperature approximately 5° less than the secondtemperature.

In another embodiment, the voltage source is varied by varying the RMSvoltage, and more particularly by varying the peak amplitude.

In other embodiments, the power scheme of the generator may also includean algorithm that delivers bipolar and monopolar power to multiple RFoutlets, and adjusts the bipolar to monopolar ratio by varying one ormore of the phase angle, voltage source, the RMS voltage and the peakamplitude. In still other embodiments, the power from the generator isdelivered in multiple fields, and each field has a set duty cyclepercentage. The duty cycle may be set between about 5 and about 25%. Insome embodiments, the generator may have a least four, or at least 12,variable power supply circuits. In some embodiments, the power from thegenerator may be delivered in multiple fields, each field having aninitial duty cycle percentage, said duty cycle percentage increasing toachieve a target temperature.

In alternate embodiments, the radiofrequency generator has at leastfour, or at least twelve variable power supply circuits.

In some embodiments, the algorithm of the power scheme delivers bipolarand/or monopolar power in sets of multiple repeating fields and thegenerator is adjusted by adjusting the ratio of monopolar fields tocombination fields and/or bipolar fields by varying the average “on”time of the bipolar and/or monopolar power delivery within each of saidsets of multiple repeating fields. The average “on” time may be adjustedby adjusting one or more of the ratio of monopolar to combination and/orbipolar fields with a set, the duty cycle ratio within one or morefields in the set, and the field length of one or more fields within theset. The RF outputs of the generator may be in-phase or out-of-phase andthe systems include a ground pad that is always electrically connected.Out-of-phase energy delivery may be accomplished with a 90° or 180°phase shift.

In some embodiments, the algorithm of the power scheme may deliver powerto multiple RF outputs with a first duty cycle percentage and increasethe duty cycle percentage to achieve a target temperature such as tomaximize the off-time portion of the duty cycle.

In some embodiments, the generator may have multiple RF outputs whichare configured to be selectively paired to deliver bipolar energybetween the selected pair.

In some embodiments, the generator may have at least four independenttemperature inputs configured to receive temperature information andproduce at least four corresponding temperature signals, and at leastfour PID loops configured to receive the at least four temperaturesignals and regulate RF power delivery.

In some embodiments, the generator may have a first set of ablationparameters configured to be utilized when a first ablation catheter isattached, and a second set of ablation parameters configured to beutilized when a second ablation catheter is attached. The powerdelivered is dependent on one or more parameters of the ablationcatheter receiving ablation energy, said parameters selected from thegroup consisting of distance between two electrodes, electrode geometry,thermocouple location and combinations thereof.

In some embodiments, the RF generator may have an EKG interface moduleconfigured to isolate an EKG monitoring unit from delivered RF energywhile minimizing attenuation of EKG signals received from the electrodesof the ablation catheter. The EKG interface module may include aninductor to attenuate the RF energy, which may have approximately 1000milliHenry of inductance.

In some embodiments, the RF generator may deliver energy in monopolar orcombination mode only such that the return pad remains electricallyconnected during energy delivery. In certain embodiments, the bipolarportion may be created with 90° or 180° phase shifted applied voltages.

In some embodiments, the generator may have a signal generator for eachtwo RF outputs. The first signal generator may be synchronized in timewith a second signal generator. Each signal generator may be undermicroprocessor control.

In some embodiments, the power from the generator may be duty cyclecontrolled, and may be adjusted in a series of discrete steps, which maybe at least 256 steps. The duty cycle period may be a period of timeless than the thermal time constant of the tissue to be ablated. Theduty cycle period may be approximately 17 milliseconds or between 10 and500 milliseconds and may be configured to be adjusted by an operator. Inanother embodiment, the duty cycle may be approximately 10%, and may bebetween about 5% and about 25%.

In some embodiments, the bipolar power delivered by the generator may becreated by a phase shift between applied voltages, said phase shiftadjustable in discrete steps, such as 16 steps. The applied voltage maybe between about 20 and 200 volts RMS, more specifically 40 volts RMS,or 100 volts RMS. In some embodiments the applied voltage has afrequency of approximately 470 KHz.

In some embodiments, power delivered by the generator maybe adjustableby an operator. In some embodiments the delivered power may beadjustable between 0 and 80 watts RMS. The delivered power may beadjusted by varying phase shift; duty cycle percentage; duty cycleperiod; applied voltage; frequency of applied voltage; shape of appliedvoltage such as sinusoidal, triangular wave, or square wave shapes;connections to the return pad; voltage applied to return pad; andcombinations thereof. The bipolar to monopolar ratio may be adjusted.The delivered power may be adjusted by microprocessor control. In otherembodiments, the power delivered by the generator is adjusted bymicroprocessor control.

In some embodiments, the generator may deliver power during a set ofrepeating fields, said fields including an “on” time and an “off.” Theset of repeating fields may include 4 or 8 fields. Each field may have aperiod between about 10 and 500 milliseconds, more specificallyapproximately 17 milliseconds. The generator may deliver power duringthe “on” time including at least one of monopolar power, bipolar power,and combination power. The power delivered during the “on” time may belimited to monopolar or combination power.

In some embodiments, the generator may have an algorithm that includesat least one power limit. The power limits may include multiple powerlimits. The first power limit may be applicable to a first ablationcatheter and a second power limit applicable to a second ablationcatheter. In another embodiment, the first power limit may be applicableto a first bipolar-monopolar ratio and a second power limit applicableto a second bipolar-monopolar ratio. The power limit for the greaterbipolar-monopolar ratio may be less than the power limit for the lesserbipolar-monopolar ratio. The power limit may be approximately 10 wattsRMS and applicable to a monopolar-only power delivery. The power limitof approximately 10 watts RMS may be applicable to a monopolar-bipolarratio of 1:1, 2:1, or 4:1. The power limit of approximately 6 watts RMSmay be applicable to a bipolar-only power delivery. A power limit ofapproximately 20 watts may be applicable to at least one electrode of anablation catheter. A power limit of approximately 30 watts may beapplicable to at least one electrode of an ablation catheter.

In some embodiments, the generator may have a return pad that iselectrically connected to a return or common connection of all the RFoutputs. The return pad may be electrically connected during all energydeliveries.

In some embodiments, the generator may provide duty cycle controlledenergy delivery and one or more measurements are performed during the“off” time of a duty cycle. The measurement may be an analysis ofinformation received from a temperature sensor. The temperature sensormay be a thermocouple of an ablation catheter. The measurement may be ananalysis of information received from an EKG sensor. The EKG sensor maybe an electrode of an ablation catheter.

In some embodiments, the generator may be configured to provideelectrical isolation between at least one component of the generator andthe patient. The electrical isolation provided may be at least 5000volts of electrical isolation. The at least one component may be an RFoutput of the generator. The generator may have a temperature inputconfigured to receive temperature information from a thermocouple, andsaid at least one component is said temperature input.

In some embodiments, the generator may have a temperature sensor moduleconfigured to receive temperature information from multiple temperaturesensors. The temperature sensor module may include at least 4, at least8, or at least 12 independent channels. The temperature sensor modulemay include multiple independent control loops configured to providefeedback to regulate power based on current temperature informationreceived from the temperature sensors and target temperature informationset by an operator of the system. In some embodiments, the targettemperature information may be selected from the range of 50° C. to 70°C. In some embodiments, the generator my have a second targettemperature, said second target temperature used in combination with thefirst target temperature by a power control algorithm of the generator.In some embodiments, the temperature sensor module may include anamplifier for each temperature input, each amplified configured toamplify the signal. The amplifier may have a gain of approximately 100.In some embodiments, the temperature ratio between the variouselectrodes may be controlled by adjusting each RF output's duty cycle,such as to balance the temperature across the lesion.

In some embodiments, the generator may have bipolar to monopolar powerdelivery controlled using time division multiplexing.

In some embodiments, the generator is configured is configured toperform cardiac procedures selected from the group consisting of atrialfibrillation procedures; supra ventricular tachycardia procedures;atrial tachycardia procedures; supra ventricular tachycardia procedures;ventricular fibrillation procedures; and combinations thereof.

In some embodiments, the generator is configured to perform tumorablation procedures.

In some embodiments, the generator is configured to perform proceduresselected from the group consisting of: prostate procedures; brainprocedures; gall bladder procedures; uterus procedures; and combinationsthereof.

In some embodiments, the generator further has at least one ablationcatheter. In some embodiments, the ablation catheter is configured toperform a pulmonary vein ablation procedure. The ablation catheter mayinclude at least one electrode with a mass between 30 and 50 milligrams,more specifically approximately 40 milligrams. The ablation catheter mayhave at least one thermocouple with a mass between 48 and 88 micrograms,more specifically approximately 68 milligrams. The ablation catheter mayinclude at least one thermocouple constructed of wire of approximately38 gauge. The ablation catheter may be configured to perform an atrialwall ablation procedure. The ablation catheter may include at least oneelectrode with a mass between 17 and 37 milligrams, more specificallyapproximately 27 milligrams. The ablation catheter may include at leastone thermocouple with a mass between 22and 62 micrograms, morespecifically 43 micrograms. The ablation catheter may include at leastone thermocouple constructed of wire of approximately 40 gauge. Theablation catheter may include at least one electrode with a wallthickness between 0.004″ and 0.010″, more specifically approximately0.006″. The ablation catheter may include at least one electrodeincluding a heat sink. The at least one electrode including a heat sinkmay be a projecting fin.

In some embodiments the generator may include a static load electricallyconnected to each RF amplifier configured to stabilize the RF output.The static load may be approximately 2000 ohms of impedance.

In some embodiments, the generator may include an algorithm whichrequires a minimum ablation energy delivery time. The minimum ablationenergy delivery time may be 25, or 40 seconds.

Another embodiment of the invention is a system for delivering energy toablate tissue of a patient, having a remote controller for theradiofrequency generator and having a radiofrequency generator. Thecontroller has a user interface configured to allow an operator to sendcommands to the radiofrequency generator or to provide to an operatorinformation received from the radiofrequency generator. The remotecontroller may both send commands and provide information to anoperator, and the commands and/or said information may be transferredover a wired or wireless connection. The remote controller may besterile, and may be a sterile bag configured to surround at least thehousing of the remote controller. The user interface may provide thesame set of commands, or may provide the same set of information, as theuser interface of the RF generator.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate various embodiments of thepresent invention, and, together with the description, serve to explainthe principles of the invention. In the drawings:

FIG. 1 illustrates a schematic depiction of an RF generator, consistentwith the present invention.

FIG. 2 illustrates details of a portion of the embodiment of FIG. 1,including a pair of RF outputs.

FIG. 3 illustrates a circuit diagram of an RF output of FIG. 2

FIGS. 4A, 4B and 4C illustrate perspective views of electrode carrierassemblies of three different ablation catheters, consistent with thepresent invention.

FIG. 5 illustrates a schematic depiction of an RF output portion of anRF generator, including multiplexed outputs, consistent with the presentinvention.

FIGS. 6A and 6B illustrate end views of electrode carrier assemblies oftwo different ablation catheters, consistent with the present invention.

FIGS. 7A and 7B each illustrate a circuit equivalent to electrode-tissueinteraction employed to demonstrate generation of bipolar and/ormonopolar currents, consistent with the present invention.

FIGS. 8A-D illustrate a power delivery scheme including four fieldsconfigured to deliver only monopolar power, consistent with the presentinvention.

FIGS. 9A-D illustrate a power delivery scheme including four fieldsconfigured to deliver a 1:1 ratio of bipolar to monopolar power,consistent with the present invention.

FIGS. 10A-D illustrate a power delivery scheme including four fieldsconfigured to deliver a 2:1 ratio of bipolar to monopolar power,consistent with the present invention.

FIGS. 11A-D illustrate a power delivery scheme including four fieldsconfigured to deliver a 4:1 ratio of bipolar to monopolar power,consistent with the present invention.

FIGS. 12A-D illustrate a power delivery scheme including four fieldsconfigured to deliver only bipolar power, consistent with the presentinvention.

FIG. 13 illustrates a schematic depiction of a temperature sensor inputportion of an RF generator, consistent with the present invention.

FIG. 14 illustrates a circuit diagram of a temperature sensor inputportion of an RF generator, consistent with the present invention.

FIG. 15 illustrates a power delivery scheme for an RF generator,consistent with the present invention.

FIG. 16 illustrates a power delivery algorithm for an RF generator,consistent with the present invention.

FIGS. 17A, 17B and 17C illustrates power delivery schemes in which thebipolar to monopolar ratio is set by varying the ratio of bipolar tomonopolar fields, consistent with the present invention.

FIGS. 18A and 18B illustrates power delivery schemes in which thebipolar to monopolar ratio is set by varying the duty cycle percentagewithin the bipolar and/or monopolar fields, consistent with the presentinvention.

FIG. 19 illustrates a power delivery scheme in which the bipolar tomonopolar ratio is set by varying the length (time) of the bipolarand/or monopolar fields, consistent with the present invention.

FIG. 20 illustrates a schematic of an exemplary embodiment forinterfacing RF outputs with an EKG diagnostic device.

FIG. 21 illustrates an exemplary remote control for an RG generator.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention provides catheters for performing targeted tissueablation in a subject. In some embodiments, the catheters comprise atubular body member having a proximal end and distal end and a lumenextending therebetween. The catheter is of the type used for performingintracardiac procedures, typically being introduced from the femoralvein in a patient's leg or from a vessel in the patient's neck. Thecatheter is introducible through a sheath and also has a steerable tipthat allows positioning of the distal portion such as when the distalend of the catheter is within a heart chamber. The catheters includeablation elements mounted on a carrier assembly. The carrier assembly isattached to a coupler, which in turn is connected to a control shaftthat is coaxially disposed and slidingly received within the lumen ofthe tubular body member. The carrier assembly is deployable byactivating one or more controls on a handle of the catheter, such as toengage one or more ablation elements against cardiac tissue, typicallyatrial wall tissue or other endocardial tissue.

Arrays of ablation elements, such as electrode arrays, may be configuredin a wide variety of ways and patterns. In particular, the presentinvention provides devices with electrode arrays that provide electricalenergy, such as radiofrequency (RF) energy, in monopolar mode, bipolarmode or combined monopolar-bipolar mode, as well as methods for treatingconditions (e.g., atrial fibrillation, supra ventricular tachycardia,atrial tachycardia, ventricular tachycardia, ventricular fibrillation,and the like) with these devices.

The normal functioning of the heart relies on proper electrical impulsegeneration and transmission. In certain heart diseases (e.g., atrialfibrillation) proper electrical generation and transmission aredisrupted or are otherwise abnormal. In order to prevent improperimpulse generation and transmission from causing an undesired condition,the ablation catheters and RF generators of the present invention may beemployed.

One current method of treating cardiac arrhythmias is with catheterablation therapy. Physicians make use of catheters to gain access intointerior regions of the body. Catheters with attached electrode arraysor other ablating devices are used to create lesions that disruptelectrical pathways in cardiac tissue. In the treatment of cardiacarrhythmias, a specific area of cardiac tissue having aberrantconductive pathways, such as atrial rotors, emitting or conductingerratic electrical impulses, is initially localized. A user (e.g., aphysician) directs a catheter through a main vein or artery into theinterior region of the heart that is to be treated. The ablating elementis next placed near the targeted cardiac tissue that is to be ablated.The physician directs energy, provided by a source external to thepatient, from one or more ablation elements to ablate the neighboringtissue and form a lesion. In general, the goal of catheter ablationtherapy is to disrupt the electrical pathways in cardiac tissue to stopthe emission of and/or prevent the propagation of erratic electricimpulses, thereby curing the focus of the disorder. For treatment ofatrial fibrillation, currently available methods and devices have shownonly limited success and/or employ devices that are extremely difficultto use or otherwise impractical.

The ablation systems of the present invention allow the generation oflesions of appropriate size and shape to treat conditions involvingdisorganized electrical conduction (e.g., atrial fibrillation). Theablation systems of the present invention are also practical in terms ofease-of-use and limiting risk to the patient (such as in creating anefficacious lesion while minimizing damage to untargeted tissue), aswell as significantly reducing procedure times. The present inventionaddresses this need with, for example, carrier assemblies with 3 or 4carrier arms, carrier assemblies with forward facing electrodes, carrierassemblies with rear-facing electrodes and carrier assemblies configuredin a helix or partial helix. The carrier assemblies include ablationelements such as electrodes which create spiral, radial, or other simpleor complex shaped patterns of lesions in the endocardial surface of theatria by delivery of energy to tissue or other means. The electrodes mayinclude projecting fins to improve cooling properties. The lesionscreated by the ablation catheters and RF generators of the presentinvention are suitable for inhibiting the propagation of inappropriateelectrical impulses in the heart for prevention of reentrantarrhythmias, while minimizing damage to untargeted tissue, such as theesophagus or phrenic nerve of the patient.

Definitions. To facilitate an understanding of the invention, a numberof terms are defined below.

As used herein, the terms “subject” and “patient” refer to any animal,such as a mammal like livestock, pets, or a human. Specific examples of“subjects” and “patients” include, but are not limited, to individualsrequiring medical assistance, and in particular, requiring atrialfibrillation catheter ablation treatment.

As used herein, the terms “catheter ablation” or “ablation procedures”or “ablation therapy,” and like terms, refer to what is generally knownas tissue destruction procedures. Ablation is often used in treatingseveral medical conditions, including abnormal heart rhythms. It can beperformed both surgically and non-surgically. Non-surgical ablation istypically performed in a special lab called the electrophysiology (EP)laboratory. During this non-surgical procedure an ablation catheter isinserted into the heart using fluoroscopy for visualization, and then anenergy delivery apparatus is used to direct energy to the heart musclevia one or more ablation elements of the ablation catheter. This energyeither “disconnects” or “isolates” the pathway of the abnormal rhythm(depending on the type of ablation). It can also be used to disconnectthe conductive pathway between the upper chambers (atria) and the lowerchambers (ventricles) of the heart. For individuals requiring heartsurgery, ablation can be performed during coronary artery bypass orvalve surgery.

As used herein, the term “ablation element” refers to an energy deliveryelement, such as an electrode for delivering electrical energy. Ablationelements can be configured to deliver multiple types of energy, such asultrasound energy and cryogenic energy, either simultaneously orserially. Electrodes can be constructed of a conductive plate, wirecoil, or other means of conducting electrical energy through contactingtissue. In monopolar energy delivery mode, the energy is conducted fromthe electrode, through the tissue to a return or ground pad, such as aconductive pad attached to the back of the patient. The highconcentration of energy at the electrode site causes localized tissueablation. In bipolar energy delivery mode, the energy is conducted froma first electrode to one or more separate electrodes, relatively localto the first electrode, through the tissue between the associatedelectrodes. Bipolar energy delivery results in more precise, shallowlesions while monopolar delivery results in deeper lesions. Bothmonopolar and bipolar delivery provide advantages, and the combinationof their use is one embodiment of this application.

As used herein, the term “carrier assembly” refers to a flexiblecarrier, on which one or more ablation elements are disposed. Carrierassemblies are not limited to any particular size, or shape, and can beconfigured to be constrained within an appropriately sized lumen.

As used herein, the term “carrier arm” refers to a wire-like shaftcapable of interfacing with electrodes and the coupler. A carrier arm isnot limited to any size or measurement. Examples include, but are notlimited to: stainless steel shafts; Nitinol shafts; titanium shafts;polyurethane shafts; nylon shafts; and steel shafts. Carrier arms can beentirely flexible, or may include flexible and rigid segments.

As used herein, the term “lesion,” or “ablation lesion,” and like terms,refers to tissue that has received ablation therapy. Examples include,but are not limited to, scars, scabs, dead tissue, burned tissue andtissue with conductive pathways that have been made highly resistive ordisconnected.

As used herein, the term “coagulum” refers to a blood mass or clot suchas a clot which may be caused by excessive heating in blood.

As used herein, the terms “return pad” or “ground pad” interchangeablyrefer to a surface electrode mounted to the patient's body, typically onthe patient's back. The return pad receives the RF ablation currentsgenerated during monopolar power delivery. The return pad is sized(large enough) such that the high temperatures generated remain within afew millimeters of the specific ablation catheter's electrode deliveringthe monopolar power.

As used herein, the term “RF output” refers to an electrical outputproduced by the RF generator of the present invention. The RF output iselectrically connected to a jack or other electromechanical connectionmeans which allows electrical connection to one or more electrodes of anablation catheter. The RF output provides the RF energy to the electrodeto ablate tissue with bipolar and/or monopolar energy.

As used herein, the term “channel” refers to a pair of RF outputsbetween which bipolar energy is delivered. Each of the RF outputs in achannel may also deliver monopolar energy (simultaneous and/orsequential to bipolar energy delivery), such as when a return pad isconnected.

As used herein, the term “targeted tissue” refers to tissue identifiedby the clinician (and/or one or more algorithms of the system) to beablated, such as to disconnect an aberrant electrical pathway causing anarrhythmia, or other undesired tissue such as cancer tissue.

As used herein, the term “untargeted tissue” refers to tissue which isdesired to avoid damage by ablation energy, such as the esophagus orphrenic nerve in an arrhythmia ablation procedure.

As used herein, the term “set ablation time” refers to a time periodover which ablation energy is delivered to targeted tissue in arelatively continuous manner, to ablate that tissue. The set ablationtime is set by the operator and/or automatically set by one or morealgorithms of the system of the present invention.

As used herein, the term “duty cycle” refers to the proportion of timeduring which a component, device or system is operated. The duty cyclecan be expressed as a ratio or as a percentage. A microwave oven is agood example of a product that uses duty cycle for power control. At,e.g., power level one, the oven will be on for one second, and then offfor nine seconds. This cycle repeats until the timer runs out. The ovenis on for one out of ten seconds, or 1/10 of the time, and its dutycycle is therefore 1/10 or 10 percent.

As used herein, the term “field” refers to a single period of a dutycycle. Each field includes an “on” time in which energy is delivered andan “off” time in which no energy is delivered. In the system of thepresent invention, a sequential set of fields (e.g. 2, 4, 8) have acustomized power delivery scheme which repeats over time.

As used herein, the term “power delivery scheme” refers to a set ofablation parameters to be delivered during a set ablation time, and usedto safely create an effective lesion in targeted tissue. Power deliveryscheme parameters include but are not limited to: type (bipolar and/ormonopolar) of energy delivered; voltage delivered; current delivered;frequency of energy delivery; duty cycle parameter such as duty cyclepercentage or length of period; field parameter such as configuration offields or number of fields in set that repeats; and combinationsthereof.

As used herein, the term “PID”, which is an acronym for “Proportional,Integral, Derivative”, refers to a type of controller that is designedto eliminate the need for continuous operator attention. Cruise controlin a car and a house thermostat are common examples of how PID-basedcontrollers are used to automatically adjust some variable to hold themeasurement at the set-point.

The present invention provides structures that embody aspects of theablation catheter. The present invention also provides RF generators forproviding ablation energy to the ablation catheters. The illustratedembodiments discuss these structures and techniques in the context ofcatheter-based cardiac ablation. These structures, systems, andtechniques are well suited for use in the field of cardiac ablation.

However, it should be appreciated that the invention is applicable foruse in other tissue ablation applications such as tumor ablationprocedures. For example, the various aspects of the invention haveapplication in procedures for ablating tissue in the prostrate, brain,gall bladder, uterus, and other regions of the body, such as regionswith an accessible wall or flat tissue surface, using systems that arenot necessarily catheter-based. In one embodiment, the target tissue istumor tissue.

The multifunctional catheters and RF generators of the present inventionhave advantages over previous prior art devices. The accompanyingfigures show various embodiments of the ablation systems of the presentinvention. The present invention is not limited to these particularconfigurations.

Specific details of electrode and array designs have been givenelsewhere, such as in U.S. application Ser. No. 10/997,172, filed Nov.24, 2004, entitled “Atrial Ablation Catheter and Method of Use”,assigned to the assignee of the present invention and hereinincorporated by reference in its entirety for all purposes. For thepurposes of FIG. 1, it is generally noted that all designs shown mayinclude multiple electrodes, and in some configurations also include areturn or ground pad (a large surface area electrode often attached tothe patient's back). At least one pair of electrodes, and often manypairs, may be activated or powered with appropriately-powered potentialdifferences to create RF waves that penetrate and ablate desired tissue.If the powering occurs between a pair of electrodes, it is termed“bipolar”. If the powering occurs between one electrode and the returnpad, it is termed “monopolar”. If both bipolar and monopolar power isdelivered simultaneously to tissue, it is termed “combo,” “combo mode”or “bipolar/monopolar mode.”

FIG. 1 shows a schematic depiction of an embodiment of the invention.System 100 includes RF generator (RFG) 10, which is attached to a powersource, to ablation catheter 90 a and also to return pad 80. A source ofpower, such as AC line voltage of 120V, 220V, etc of single or multiplephase, or a DC source such as an electrochemical battery, is coupled toablation catheter 90 a through RF generator (RFG) 10. In an alternativeembodiment, the power source, such as the electrochemical battery, isintegral to RFG 10, such as to support ambulatory use such as on abattlefield. RFG 10 provides ablation energy to one or more ablationcatheters by sending power to one or more independently controlled RFoutputs 31 included in RF bank 30. The independent control of each RFoutput allows a unique, programmable power delivery signal to be sent toeach electrode of an ablation catheter. The independent control of eachRF output further allows unique (independent) closed loop powerdelivery, such as power delivery regulated by tissue temperatureinformation received from one or more temperature sensors integral tothe attached ablation catheter and/or from sensors included in aseparate device.

A multiple wire cable 92 attaches RF bank 30 to the electrodes ofablation catheter 90 a via electrode connection 91. (The electrodes arenot shown but may be metal plates with or without projecting fins thatconnect to electrode connection 91 via individual wires.) In oneembodiment, RF bank 30 includes twelve separate, electrically-isolatedRF outputs, grouped into two outputs per channel (six channels total).Each RF output 31 is configured to provide monopolar, bipolar or acombination of monopolar and bipolar currents simultaneously. The numberof RF outputs can vary as required by the design. In one embodiment,four to twelve independent RF outputs are provided, such as when thesystem of the present invention includes a kit of ablation cathetersincluding at least one catheter with from four to twelve electrodes. Inanother embodiment, more than 16 independent RF outputs are provided,such as when the system of the present invention includes a kit ofablation catheters including at least one catheter with sixteenelectrodes.

Monopolar delivery is accomplished by delivering currents that travelfrom an RF output 41 of bank 40 to an electrically attached electrode ofan ablation catheter, through tissue to return pad 80, and back to RFGthrough connection 11 to which return pad 80 has been connected. Bipolardelivery is accomplished by delivering current between a first RF output41 which has been electrically connected to a first electrode of anablation catheter and a second RF output 41 which has been electricallyconnected to a second electrode of the ablation catheter, the currenttraveling through the tissue proximate the first and second electrodes.Combo mode energy delivery is accomplished by combining the monopolarand bipolar currents described immediately hereabove.

In one embodiment, simultaneous monopolar and bipolar currents aredelivered by utilizing a constant voltage source for all pairs of RFoutputs (channels). Varying the voltage phase angle between the pairedelectrodes can be used to adjust the magnitude of power delivered aswell as adjust the ratio of monopolar to bipolar power delivery. Theuser (e.g. a clinician or clinician's assistant) may select or deselectRF outputs receiving energy to customize therapeutic delivery to anindividual patient's needs. In another embodiment, a variable voltagesource is applied to the RF outputs. In this embodiment, the voltagephase angle may be fixed (e.g. 0° phase difference for monopolar and180° phase difference for bipolar). Alternatively, in addition tovarying the voltage, the phase angle may be varied. When the phase angleis fixed, the ratio of bipolar to monopolar (or combo to monopolar) maybe varied by other means, such as by adjusting the ratio of “cumulative”delivery times of the monopolar versus bipolar (or combo) currents(described in detail in reference to FIGS. 17A-17C, 18A-18B and 19herebelow).

In another embodiment, five different pre-set energy delivery optionsare provided to the user: monopolar-only, bipolar-only, and 4:1, 2:1 and1:1 bipolar/monopolar ratios. A bipolar-only option provides theshallowest depth lesion, followed by 4:1, then 2:1, then 1:1 and thenmonopolar-only which provides the deepest depth lesion. The ability toprecisely control lesion depth increases the safety of the system andincreases procedure success rates as target tissue can be ablated nearor over important structures. In an alternative embodiment, currents aredelivered in either monopolar mode or combo mode (only). The embodimentwhich avoids bipolar-only, has been shown to provide numerous benefitsincluding reduction of electrical noise generated by switching off thereturn pad circuit (e.g. to create bipolar-only mode).

In another embodiment, RFG 10 includes multiple independent PID controlloops that utilize measured tissue temperature information to regulate(i.e. provide closed loop) energy delivered to an ablation catheter'selectrodes. A multiple wire cable 94 attaches temperature sensor inputbank 40 to the thermocouples of ablation catheter 90 a via thermocoupleconnection 93. (The thermocouples are not shown but may be integral tothe electrodes of ablation catheter 90 a and electrically connected tothermocouple connection 93 via one or more wires.) In one embodiment,multiple wire cable 92 and multiple wire cable 94 are a single conduit.The PID control loops of RFG 10 receive the temperature information viatemperature sensor inputs 41 of bank 40. In one embodiment, temperaturesensor input bank 40 includes twelve separate, electrically-isolatedtemperature sensor inputs. Each temperature input 41 is configured toreceive temperature information such as from a sensor such as athermocouple. The number of temperature inputs can vary as required bythe design. In one embodiment, four to twelve independent inputs areprovided, such as when the system of the present invention includes akit of ablation catheters including at least one catheter with from fourto twelve thermocouples. In another embodiment, more than 16 independenttemperature inputs are provided, such as when the system of the presentinvention includes a kit of ablation catheters including at least onecatheter with at least sixteen thermocouples.

Ablation target temperatures are user-selectable and automaticallyachieved and maintained throughout lesion creation, regardless of bloodflow conditions and/or electrode contact scenarios. Temperature targetinformation is entered via user interface 20 of RFG 10. User interface20 may include a touch screen display, a membrane keypad or other userinput components integral to or separate from a housing of RFG 10 (referto FIG. 21 for a separate remote control configuration). User interface20 also includes user output components such as text and graphic displayscreens, indicator lights and other user output components integral toor separate from a housing of RFG 10. User interface 20 is configured toallow an operator to input system parameter and output configurationinformation including but not limited to: electrode selection; powerdelivery settings, targets and other power delivery parameters; andother information. User interface 20 is further configured to provideinformation to the operator, such as visual and audible informationincluding but not limited to: electrode selection, power deliveryparameters and other information. Automatic temperature-controlledlesion creation provides safety and consistency in lesion formation.Typical target temperature values made available to the operator rangefrom 50 to 70° C.

In the system of one embodiment, in order to regulate power across anumber of separate RF outputs 31 that utilize phase angle differences togenerate bipolar currents, the utilization of a constant voltage source,in conjunction with variable duty cycle power delivery, greatlysimplifies the control and regulation of power. Utilizing duty cyclepower control also provides the ability to deliver high peak powerswhile providing electrode cooling time during the off-portion of theduty cycle. Duty cycle control is configured such that the period (“on”time plus “off” time) is much less than the thermal time constant of thetissue, such that the tissue acts as an “integrator”, continuouslyaccumulating the heat energy while the electrodes of the ablationcatheter cool during the off period. In one embodiment, the period ofeach duty cycle is approximately 17 msec, and the thermal time constantis much longer than 17 msec. Allowing the electrodes to cool during theoff period, reduces tissue overheating which could result in “popping”or micro-explosions within the tissue, or other undesired tissuebreakdown. Duty cycle periods of approximately 17 msec are applicable tothe system of the present invention. Duty cycle periods that are toolong result in inadequate ablation of targeted tissue. Duty cycleperiods that are too short result in inadequate cooling which may causechar or other blood clots, or damage untargeted tissue. In alternativeembodiment, the duty cycle periods may range from 10 msec to 500 msec,and may be adjustable by the operator of the RFG via, e.g., the userinterface. Duty cycle energy delivery provides increased efficiency,effectiveness and safety during lesion creation at reduced RMS powerlevels.

In some embodiments, amplitude control may replace or work inconjunction with duty cycle control. If a fixed duty cycle isimplemented, e.g. a 10% duty cycle, the voltage may be regulated (to anamplifier of each RF output 31), such as voltage regulated by thetemperature PID loops described above to similarly achieve a targettissue temperature in a precise manner. In an additional embodiment ofthis varied voltage configuration, if the temperature or power limit cannot be reached with a given, pre-set duty cycle, the duty cyclepercentage can be increased (e.g. in small steps) until equilibrium isachieved (i.e. the varied voltage, varied duty cycle embodimentmentioned above). The duty cycle percentage chosen provides a powerlimit (as well as bipolar to monopolar power ratios), and thetemperature achieved is regulated by varying RF amplitude (voltage)delivered to RF outputs 31, in monopolar, bipolar, or combo mode energydelivery. In one embodiment, the temperature ratio between the variouselectrodes can be controlled by adjusting each RF output's duty cycle,such as to balance the temperature across the lesion. By starting with alow duty cycle on-time percentage, and increasing as necessary, powerdelivery equilibration may be achieved while maximizing the off-timepercentage. Maximizing the off-time percentage provides numerousadvantages including optimized electrode cooling and tissue temperatureequilibrating, as well as maximizing the time that electronicmeasurements can be made during the low-noise off-time, such as EKGmapping and thermocouple measurements. In some embodiments, this variedvoltage control configuration involves the addition of 12 separatevariable power supply circuits on RF circuit boards of RFG 10, such asto work with ablation catheters including up to 12 electrodes. The dutycycle percentage is typically set in the range of 5% to 25% dependingupon the (tissue) load resistance and power required for adequateablation. This voltage-varied configuration is an alternative method ofpower control that can give the same or similar clinical effects to theduty cycle power control described above.

Referring back to FIG. 1, system 100 further includes ablation catheter90 b and ablation catheter 90 c, each of which is configured to attachto RF output bank 30 and temperature sensor input bank 40 for energydelivery and temperature feedback similar to that described above inreference to ablation catheter 90 a. Ablation catheters 90 a, 90 b and90 c may be of the construction described herebelow in reference toFIGS. 4A, 4B and 4C respectively. Alternative or additional ablationcatheters may be included in the system of the present invention.

More details on the system of the present invention are provided below.

Referring to FIG. 2, power from the power source of FIG. 1 is used todigitally generate a high-power, low-voltage, low-frequency square wave.FIG. 2 illustrates two parallel circuits which produce a first RF output31 a and a second RF output 31 b, such as a pair of RF outputs (achannel)—used to deliver bipolar energy to a pre-determined pair ofelectrodes on an ablation catheter. The parallel circuits for RF output31 a and RF output 31 b include half-bridge circuits 32 a and 32 b,series resonant circuits 33 a and 33 b, and output transformers 34 a and34 b, respectively. Half-bridge circuits 32 a and 32 b each receive adrive signal from signal generator 35, such as a programmable logicdevice (PLD). Signal generator 35 receives control signals from amicroprocessor of the RFG of the present invention.

Half bridge circuits 32 a and 32 b each produce a square wave, e.g. a24-volt peak-to-peak square wave. Series resonant circuits 33 a and 33 beach couple the high power square wave to output transformers 34 a and34 b respectively. Output transformers 34 a and 34 b each is anisolation transformer configured to provide both patient electricalisolation and the voltage step-up required to ablate tissue. In moredetail, the ablation electrodes are at patient potential, and 5000-6000volts isolation is provided between the electrodes and earth ground.Since the input is at chassis ground, output transformers 34 a and 34 beach is configured to provide 5000-6000 volts isolation between itsprimary and secondary coils. An additional advantage of this isolationcircuitry is that power can be measured without the need to isolate themeasuring devices. A portion of the applicable circuitry is shown inFIG. 3.

Series resonant circuits 33 a and 33 b each convert the square warereceived from half bridge circuits 32 a and 32 b respectively, to a sinewave. These conversions are accomplished by maximizing energy couplingat the fundamental frequency chosen, e.g., at 470 kHz. This power outputconfiguration is over 95% efficient in converting the 24 VDC input powerto RF energy, as the output transformer has an efficiency close to 100%.In this configuration, half-bridge circuit 32 a and 32 b, seriesresonant circuit 33 a and 33 b and output transformer 34 a and 34 b, areconfigured to convert signal generator's 45 470 kHz logic level signalto two 100 VAC sine waves, each capable of delivering 100 watts. Inaddition, it is noted that by measuring power inputted (P_(input)),outputted power (P_(output)) may be obtained. In one embodiment, acurrent-sensing resistor is employed (not shown, but having a precise,known resistance) so inputted current (I_(in)) can be determined by thesystem. Since inputted voltage (V_(in)) is also known, as the powersupply precisely regulates this, the system can determine P_(in) andthus P_(output).

As noted above, the system employs a frequency of 470 kHz (orapproximately 470 kHz, noting that 500 kHz is not used as it may bereserved for a public emergency band.) The 470 kHz is generated by aPLD, signal generator 35. In particular, an oscillator provides (startswith) a higher frequency, which is then divided down to 470 kHz. The 470kHz waveform may be generated in numerous configurations, such as with0° phase or any other phase, such as a phase determined in 250 steps ordivisions. In one embodiment, the signal for the PLD is a 5-volt digitalsignal with the phase information “built-in”. Signal generator 35 alsogenerates the opposite polarity signal which may also be used to driveone or more field effect transistors (FETs) integral to half bridgecircuit 32 a and 32 b. Signal generator 35 provides a synchronizationpulse, not shown but connected to the signal generators of subsequentpairs of RF outputs also not shown; such that all the signal generatorsof the RFG are in synchrony (i.e. signal generator 35 is the “master”).

In one embodiment, an RF circuit board includes two circuits of FIG. 2,i.e. two signal generator 35's, four half bridge circuits 32's, fourseries resonant circuits 33's and four output transformers 34's,producing four RF outputs (or two channels). In this configuration, 2 RFboards would provide 8 RF outputs and 3 RF boards would provide 12 RFoutputs.

Signal generator 35 is under microprocessor control. In one embodiment,the microprocessor can set the duty cycle from all “off” to all “on” inat least 16 steps, and possibly 256 steps. In another embodiment, themicroprocessor can adjust the phase of the RF output can be set from 0°to 180° in at least 4 steps, and possibly 16 steps. This adjustabilityallows the energy to flow to pairs of electrodes in the following ways:all monopolar from the electrodes to the return pad; all bipolar betweenthe electrodes; and a combination of bipolar and monopolar with theratio set by the phase difference between the electrodes.

Referring now to FIG. 3, a schematic of one configuration of an RFoutput circuit is illustrated. Possible values for components are listedon the figure. Transformer T1 is an isolation transformer. Resistor R2,e.g., approximately 2000 ohms, provides a static load across the RFamplifier circuitry and improves the stability of the signal duringlight load conditions.

Referring now to FIG. 4A, a distal portion of an ablation catheter ofthe system of the present invention is illustrated. Carrier assembly 210a includes a single carrier arm 211 a with multiple electrodes 220 a(e.g. 10 electrodes) mounted along its length. Each electrode isconstructed of a conductive material, such as platinum, and typicallyhas a mass between 20 and 50 milligrams, or between 30 and 40milligrams. Each electrode 220 a may include a thermocouple, not shown,but integral to electrode 220 a and proximate the tissue contactingsurface of electrode 220 a. The thermocouples may be small massthermocouples, typically less than 200 micrograms or less than 100micrograms, such as to provide fast and accurate tissue/electrodeinterface temperatures. In one embodiment, the thermocouples integral toelectrodes 220 a are made of 38 gauge wire and have a mass between 48and 88 micrograms, typically 68 micrograms. Carrier assembly 210 a canbe adjusted to transition between a near-linear geometry to thenear-helical geometry shown in FIG. 4A. Carrier assembly 210 a may beconfigured for making contact with a pulmonary vein ostium of a patient.

Referring now to FIG. 4B, a distal portion of an ablation catheter ofthe system of the present invention is illustrated. Carrier assembly 210b includes multiple electrodes 220 b (e.g. 8 electrodes) mounted to fourcarrier arms 211 b arranged in an umbrella configuration. The tissuecontacting portion of electrodes 220 b face away from the proximal endof the ablation catheter such that pushing forward carrier assembly 210b advances the tissue contacting portion of electrodes 220 b intotissue. Each electrode is constructed of a conductive material, such asplatinum, and typically has a mass between 17 and 37 milligrams, such asapproximately 27 milligrams. Each electrode 220 b may include athermocouple, not shown, but integral to electrode 220 b and proximatethe tissue contacting surface of electrode 220 b. The thermocouples maybe small mass thermocouples, typically less than 200 micrograms or lessthan 100 micrograms, such as to provide fast and accuratetissue/electrode interface temperatures. In one embodiment, thethermocouples integral to electrodes 220 b are made of 40 gauge wire andhave a mass between 22 and 62 micrograms, typically 42 micrograms. Eachelectrode 220 b may include a projecting fin as shown, configured toprovide a heat sink into circulating blood. Carrier assembly 210 b canbe adjusted to transition between a near-linear geometry to the umbrellageometry shown in FIG. 4B. Carrier assembly 210 b may be configured formaking contact with the far wall of the left or right atrium of theheart of a patient.

Referring now to FIG. 4C, a distal portion of an ablation catheter ofthe system of the present invention is illustrated. Carrier assembly 210c includes multiple electrodes 220 c (e.g. 12 electrodes) mounted tothree carrier arms 211 c arranged in an umbrella configuration. Thetissue contacting portion of electrodes 220 c face toward the proximalend of the ablation catheter such that pulling carrier assembly 210 cadvances the tissue contacting portion of electrodes 220 c into tissue.Each electrode is constructed of a conductive material, such asplatinum, and typically has a mass between 17 and 37 milligrams, such asapproximately 27 milligrams. Each electrode 220 c may include athermocouple, not shown, but integral to electrode 220 c and proximatethe tissue contacting surface of electrode 220 c. The thermocouples maybe small mass thermocouples, typically less than 200 micrograms or lessthan 100 micrograms, such as to provide fast and accuratetissue/electrode interface temperatures. In one embodiment, thethermocouples integral to electrodes 220 c are made of 38 gauge wire andhave a mass between 48 and 88 micrograms, typically 68 micrograms. Eachelectrode 220 c may include a projecting fin as shown, facing away fromthe proximal end of the ablation catheter and configured to provide aheat sink into circulating blood. Carrier assembly 210 c can be adjustedto transition between a near-linear geometry to the umbrella geometryshown in FIG. 4C. Carrier assembly 210 c may be configured for makingcontact with the septum of the left atrium of the heart of a patient.

The ablation catheters of FIGS. 4A, 4B and 4C are each ablationcatheters configured to receive energy from the RF generator of thepresent invention. Additional and/or alternative catheters may also beconfigured to receive energy from the RF generator of the presentinvention. Each of the ablation catheters of FIGS. 4 a, 4B and 4C mayinclude a thermocouple within each electrode. Alternatively oradditionally, one or more carrier arms include a thermocouple along itslength, such as midway between two electrodes. Placement of thethermocouple in the electrode is such that during ablation,thermocouples are located directly over the target tissue at a distanceseparated by the electrode wall thickness only (such as a wall thicknessof 0.006″ or alternatively a wall thickness ranging from 0.004″ to0.010″). The combination of thermocouple location, size and mountingmethods provides fast and accurate tissue/electrode interfacetemperatures. Type T thermocouples (copper/constantan) may be employedas the temperature accuracy curve for type T is essentially linearwithin the temperature range used by the ablation system, i.e., bodytemperature through 80° C.

Referring now to FIG. 5, another configuration of the present inventionis illustrated in which the RF Generator's independent RF outputs can beselectively connected to the electrodes of one or more ablationcatheters. Multiple outputs transformers, such as output transformer 34a, each of which produces an independent RF output, such as RF output 31a, are connected to multiplexer 36. Multiplexer 36 includes circuitry toselectively connect each RF output to one of a bank of connections, eachof which is electrically connected to one or more electrodes of anablation catheter. Via a user interface of the RF generator, not shown,the operator can select which RF outputs are connected to whichelectrodes, such as to deliver bipolar or combo energy to any pair ofelectrodes.

Referring additionally to FIGS. 6A and 6B, arrays of electrodes on thecarrier assemblies of two different ablation catheters are illustrated.In FIG. 6A, carrier assembly 210 a includes four carrier arms 211 a onwhich eight electrodes are fixedly mounted. In FIG. 6B, carrier assembly210 b includes three carrier arms 211 b on which twelve electrodes arefixedly mounted. Using the multiplexing circuitry of FIG. 5, any pairsof electrodes may receive bipolar energy such as electrode pair “1-2” or“2-4” of carrier assembly 210 a of FIG. 6A, or electrode pair “3-4” or“4-12” of carrier assembly 210 b of FIG. 6B. All combinations of energydelivery are enabled by the independent control of each RF outputcombined with the electrode selectivity provided by multiplexer 36 andassociated circuitry of FIG. 5. The energy delivered can be customizedbased on individual patient requirements. In one configuration, energydelivery may start on the outermost electrodes (e.g. 1, 3, 6 and 8 ofFIGS. 6A and 1, 5 and 9 of FIG. 6B), and drive power to the center. Inanother configuration, the centermost electrodes (e.g. 2, 4, 5 and 7 ofFIGS. 6A and 4, 8 and 12 of FIG. 6B) receive energy simultaneously. Inyet another configuration, the linearly aligned electrodes of FIG. 6A orFIG. 6B deliver energy to produce a circular lesion. In yet anotherconfiguration, a first electrode mounted to a first carrier armtransmits bipolar energy to a second electrode mounted to a secondcarrier arm.

Referring now to FIGS. 7A and 7B, two schematic representations ofmultiple electrode assemblies and a return pad each in contact withpatient tissue are shown. Referring for FIG. 7A, if four separate RFoutputs of the same voltage and phase were connected to Electrode 1,Electrode 2, Electrode 3, and Electrode 4, and the return pad connectedto RF Generator ground, there would be current flow through tissueportions T1, T2, T3 and T4. There would be zero current flow throughtissue portions T5, T6 and T7. On the other hand, if four separate RFoutputs of all different voltages were connected to Electrode 1,Electrode 2, Electrode 3, and Electrode 4 and the return pad wasdisconnected (i.e. not connected to RF generator ground), there would becurrent flow through tissue Portions T5, T6 and T7. Due to thedisconnected ground pad, there would be no current flow through tissueportions T1, T2, T3 and T4. Finally, if four separate RF outputs of thesame voltage were connected from Electrode 1, Electrode 2, Electrode 3,and Electrode 4 to the return pad, and there were phase differencesbetween each electrode, there would be current flow through tissueportions T1, T2, T3 and T4 and there would also current flow throughtissue portions T5, T6 and T7.

EXAMPLE Combination Monopolar-Bipolar RF Delivery Method

In the example shown in FIG. 7B, if there were 40 volts RMS deliveredbetween Electrode 5 and the return pad 0° phase, and 40 volts RMSdelivered between Electrode 6 and the return pad at 180° phase, thentissue portions T8 and T9 would have 40 RMS volts across them resultingin a power in each tissue portion of 16 watts RMS(Power=V²/R=(40×40)/100)—where each tissue portion is modeled at 100ohms of impedance). The phase difference between Electrode 5 andElectrode 6 would cause a potential difference of 80 volts. Theresulting power across tissue portion T10 would be 64 watts RMS.(Power=V²/R=(80×80)/100). By varying the phase difference betweenElectrode 5 and Electrode 6 from 0° to 180°, the power delivered can bevaried from 0 to 80 watts RMS.

In one embodiment, the generation of the combined bipolar and monopolarcurrents is achieved by varying the phase, as described above. In analternative embodiment, the combined bipolar and monopolar currents aredetermined by time-division multiplexing and/or by alternating monopolarand bipolar fields, as will be described in detail in reference tosubsequent figures.

In one exemplary system, repeating duty cycle fields are employed, eachfield having a similar period (duration) and each field including an“on” portion and an “off” portion. A possible field period isapproximately 17 msec. During the on period, 20-100 volts RMS (typically100 volts RMS) is delivered to the tissue. During the off period, theoutput of the channel is disconnected from the load. In one embodiment,a sequence of four specific duty cycle fields that repeat are provided.A first field includes monopolar energy delivery only followed by an offperiod; the second field includes combined monopolar and bipolardelivery (combo) followed by an off period; the third field includesmonopolar energy delivery only followed by an off period; and the fourthfield includes monopolar and bipolar delivery (combo), with oppositephase from that of field 2, followed by an off period. In oneembodiment, by selecting the phase difference during a field, the ratiobetween bipolar and monopolar energy delivery can be varied from 4-to-1to all-monopolar. Also, by switching off the connection to the returnpad, and setting the phase shift to 180°, an all-bipolar mode can beproduced.

Phasing Sequences

In one embodiment, the ablation signal delivered to each electrode pairfrom two associated RF outputs (channel) includes four fields (e.g. eachof 17 ms period), the four fields repeating until ablation energydelivery is terminated. Each field is divided into an “on” time and an“off” time. This duty cycle ratio controls the amount of power deliveredduring each field by that RF output pair (channel). In one embodiment,during the “on” time, 100 volts RMS (at 470 kHz) is delivered to theload. During the “off” time, the output is floating, thus zero power isdelivered. For example, a duty cycle of 10% would cause a power of 10watts RMS to be delivered into a 100 ohm load during the duty cycleperiod (e.g. a field with 17 msec duration). If the voltages to the twoelectrodes are at a 0° phase difference, the bipolar voltage differenceis zero volts and therefore only monopolar currents will be delivered.If the phase difference is 90°, the bipolar voltage difference is 1.414times the monopolar voltage (E_(MONOPOLAR)), thus the power delivered istwice the monopolar power, as shown in the equation:

Power=E ² /R=(1.414*E _(MONOPOLAR))² /R=2*(E _(MONOPOLAR))² /R

If the phase difference is 180°, the voltage difference is 2 times themonopolar voltage, thus the power delivered is four times the monopolarpower, as shown in the equation:

Power=E ² /R=(2*E _(MONOPOLAR))² /R=4*(E _(MONOPOLAR))² /R

If the return pad is off, then only bipolar currents will be delivered.Field sequences such as are shown in FIGS. 8-12 may be used to achievevarious bipolar to monopolar power ratios.

During each field, each RF output pair (channel) may deliver RF power inmonopolar, bipolar or combo energy delivery. Each field may include “on”time ratios (monopolar, bipolar or combo) from 0% to 100% of the dutycycle period, typically 17 msec. In one embodiment, each energy deliveryincludes at least monopolar energy delivered, avoiding the need todisconnect the return pad. Continuous connection of the return padavoids generation of electrical noise, and allows the inclusion ofsafety detection circuitry which requires connection of the return pad.

Referring now to FIG. 8, a repeating sequence of four fields configuredto deliver monopolar power (only) to an RF output pair, or channel, isillustrated. The RF output pair receiving energy is connected to a pairof electrodes on an attached ablation catheter. During the “on” time,typically 100 volts RMS (at 470 kHz) is delivered to the tissue (load)in contact with the electrodes of the ablation catheter. During the“off” time, the output is floating, thus zero power is delivered. Thereturn pad is connected during all four fields, maintained at 0 voltsand receives the monopolar currents from each electrode deliveringmonopolar energy. Typically, all four fields have a 17 msec duty cycleperiod. The four fields repeat until the set ablation time is reached,or an alarm or alert condition is identified. All four fields have 0°phase shift between the two RF outputs (no bipolar energy delivery)causing monopolar energy to be delivered to the tissue in contact withthe electrode pair during each of the four fields.

Referring now to FIG. 9, a repeating sequence of four fields configuredto deliver a 1:1 ratio of bipolar to monopolar power to an RF outputpair, or channel, is illustrated. The RF output pair receiving energy isconnected to a pair of electrodes on an attached ablation catheter.During the “on” time, typically 100 volts RMS (at 470 kHz) is deliveredto the tissue (load) in contact with the electrodes of the ablationcatheter. During the “off” time, the output is floating, thus zero poweris delivered. The return pad is connected and maintained at 0 voltsduring all four fields, and receives the monopolar currents from eachelectrode delivering monopolar energy. Typically, all four fields have a17 msec duty cycle period. The four fields repeat until the set ablationtime is reached, or an alarm or alert condition is identified. Field 1and Field 3 have 0° phase shift between the two RF outputs (no bipolarenergy delivery) causing monopolar energy to be delivered to the tissuein contact with the electrode pair during the “on” time of Field 1 andField 3. Field 2 and Field 4 have a 90° phase shift between the two RFoutputs such that bipolar energy is delivered between the electrodesconnected to the two RF outputs. Since the return pad is connected (asit is in Fields 1 and 3), monopolar energy is also delivered in Fields 2and 4 (combo mode). As has been described above, the 90° phase shiftcauses twice the amount of bipolar energy as monopolar energy to bedelivered, during that field where both are delivered. With the dutycycle percentage held constant in all four fields (same “on” time versus“off” time ratio), the bipolar power delivered in two fields (Fields 2and 4 with the 90° phase shift) equates to the same power delivered infour fields of monopolar power delivery (Fields 1-4), thus the 1:1ratio.

Referring now to FIG. 10, a repeating sequence of four fields configuredto deliver a 2:1 ratio of bipolar to monopolar power to an RF outputpair, or channel, is illustrated. The RF output pair receiving energy isconnected to a pair of electrodes on an attached ablation catheter.During the “on” time, typically 100 volts RMS (at 470 kHz) is deliveredto the tissue (load) in contact with the electrodes of the ablationcatheter. During the “off” time, the output is floating, thus zero poweris delivered. The return pad is connected and maintained at 0 voltsduring all four fields, and receives the monopolar currents from eachelectrode delivering monopolar energy. Typically, all four fields have a17 msec duty cycle period. The four fields repeat until the set ablationtime is reached, or an alarm or alert condition is identified. Field 1and Field 3 have 0° phase shift between the two RF outputs (no bipolarenergy delivery) causing monopolar energy to be delivered to the tissuein contact with the electrode pair during the “on” time of Field 1 andField 3. Field 2 and Field 4 have a 180° phase shift between the two RFoutputs such that bipolar energy is delivered between the electrodesconnected to the two RF outputs. Since the return pad is connected (asit is in Fields 1 and 3), monopolar energy is also delivered in Fields 2and 4 (combo mode). As has been described above, the 180° phase shiftcauses four times the amount of bipolar energy as monopolar energy to bedelivered, during that field where both are delivered. With the dutycycle percentage held constant in all four fields (same “on” time versus“off” time ratio), and four times the bipolar power delivered asmonopolar in Fields 2 and 4, two fields of bipolar at a 180° phase shift(Fields 2 and 4) equates to twice the power delivered in four fields ofmonopolar (Fields 1-4), thus the 2:1 ratio.

Referring now to FIG. 11, a repeating sequence of four fields configuredto deliver a 4:1 ratio of bipolar to monopolar power to an RF outputpair, or channel, is illustrated. The RF output pair receiving energy isconnected to a pair of electrodes on an attached ablation catheter.During the “on” time, typically 100 volts RMS (at 470 kHz) is deliveredto the tissue (load) in contact with the electrodes of the ablationcatheter. During the “off” time, the output is floating, thus zero poweris delivered. The return pad is connected and maintained at 0 voltsduring all four fields, and receives the monopolar currents from eachelectrode delivering monopolar energy. Typically, all four fields have a17 msec duty cycle period. The four fields repeat until the set ablationtime is reached, or an alarm or alert condition is identified. Allfields (1-4) have a 180° phase shift between the two RF outputs suchthat bipolar energy is delivered between the electrodes connected to thetwo RF outputs. Since the return pad is connected, monopolar energy isalso delivered in all fields (combo mode). As has been described above,the 180° phase shift causes four times the amount of bipolar energy asmonopolar energy to be delivered, during that field where both aredelivered. Since all the fields are configured the same, the 4:1 ratiois delivered.

Referring now to FIG. 12, a repeating sequence of four fields configuredto deliver only bipolar power to an RF output pair, or channel, isillustrated. The RF output pair receiving energy is connected to a pairof electrodes on an attached ablation catheter. During the “on” time,typically 100 volts RMS (at 470 kHz) is delivered to the tissue (load)in contact with the electrodes of the ablation catheter. During the“off” time, the output is floating, thus zero power is delivered. Thereturn pad is disconnected, preventing monopolar energy delivery.Typically, all four fields have a 17 msec duty cycle period. The fourfields repeat until the set ablation time is reached, or an alarm oralert condition is identified. All fields (1-4) have a 180° phase shiftbetween the two RF outputs such that bipolar energy is delivered betweenthe electrodes connected to the two RF outputs. Since the return pad isdisconnected, no monopolar energy is delivered in any field.Alternatively, the RF generator can be operated in bipolar-only modewith the return pad can be left connected by adjusting the phase anglessuch that ensure that all current flows only between the ablationelectrodes and none flows to the return pad.

In FIGS. 8-11, all fields include monopolar power delivery such that thereturn pad is never switched off. The power delivery schemes illustratedin FIGS. 9-12 utilize a phase shift adjustment between two RF outputs tocontrol the ratio of bipolar to monopolar power delivery. The system ofthe present invention is configured to independently provide similar ordissimilar fields of energy delivery to other provided channels, such asRF output pairs connected to 4, 8, 12, 16 or more electrodes of anablation catheter. Additional variables may be controlled to modify thebipolar-monopolar ratio, total power delivered, or other outputparameter, such variables including but not limited to: duty cyclepercentage; duty cycle period; applied voltage; frequency of appliedvoltage; shape of applied voltage such as sinusoidal, triangle wave orsquare wave; connection to the return pad; voltage applied to returnpad; and combinations thereof.

The system of the present invention allows independent phase control ofeach RF output (e.g. up to 16 outputs or more), providing moresophisticated power delivery as compared to a previously developedsystem in which every other channel was driven at the same phase andeach RF output drove two electrodes. Each of the RF outputs can bedriven up to a maximum power, and ablation energy can be sent to each RFoutput simultaneously or sequentially. The ability to control the phaseof each electrode relative to the other electrodes enables the system togenerate bipolar currents as well as monopolar, as well as variouscombinations of these.

In the system of the present invention, each RF channel may utilizeindependent PID loops which process temperature information (e.g.temperature information received from a thermocouple mounted in eachelectrode) to modify the power delivery to that pair of RF outputs.These PID loops provide more accurate temperature-driven energy deliverythan previously developed systems. One previously developed systemdelivered power to 12 electrodes based on temperature feedback fromthree zones. The electrodes were regulated to the highest temperature inthe zone, which resulted in some of the electrodes ablatinginefficiently (e.g. not enough power delivered).

Referring now to FIG. 13, an exemplary embodiment of temperature sensorinput circuitry is illustrated. Twelve separate, isolated, temperatureacquisition modules include twelve thermocouple amplifiers, 43 a, 43 b,43 c, etc, which are configured to electrically connect to up to twelvethermocouples of one or more ablation catheters of the presentinvention. The thermocouples may be small mass thermocouples, typicallyless than 200 micrograms or less than 100 micrograms, such as to providefast and accurate tissue/electrode interface temperatures. The twelvethermocouple amplifiers 43 a, 43 b, 43 c, etc are electrically connectedto a twelve channel analog to digital (A/D) converter 42. A/D converter42 is electrically connected to microprocessor module 15. An RS-232module 16 is electrically connected to microprocessor module 15.

Fast and accurate temperature acquisition is important in delivering theproper amount of RF energy (i.e. closed-loop control). Too much (high)energy delivery can cause coagulum and/or damage adjacent tissues andstructures such as the phrenic nerve or the esophagus of the patient.Too little energy delivery can result in poor lesion creation and lowtherapeutic success rates. The system of the present invention providesenough RF energy to create a cardiac electrical conduction block withoutaffecting adjacent tissues or structures. In order to acquire fast andaccurate temperatures, the thermocouple mass is kept small and one ormore electrodes are welded directly to the inside diameter of each ofthe electrodes of each ablation catheter. Placement of the thermocouplein the electrode is such that during ablation, thermocouples are locateddirectly over the target tissue at a distance separated by the electrodewall thickness only (such as a wall thickness of 0.006″ or alternativelya wall thickness ranging from 0.004″ to 0.010″). The combination ofthermocouple location, size and mounting methods provides fast andaccurate tissue/electrode interface temperatures. Type T thermocouples(copper/constantan) may be employed as the temperature accuracy curvefor type T is essentially linear within the temperature range used bythe ablation system, i.e., body temperature through 800C.

All thermocouples located on the ablation electrodes are at patientpotential. 5000 volts of isolation is needed between the thermocouplesand earth ground in order to meet patient safety regulations (e.g. IEC601-2). The twelve temperature modules are read by microprocessor module15 which is powered by a dc-to-dc converter with the proper voltageisolation. An RS232 serial data string is isolated with anopto-isolator. Since the RF power output is duty cycle-controlled, thetemperature readings can be synchronized to the “off” period of eachfield. The synchronizing pulse is also supplied through anopto-isolator.

Referring additionally to FIG. 14, a schematic of a thermocoupleamplifier circuit is shown. Each temperature module makes use of a trueinstrumentation amplifier with a precision DC gain of 100 and severalpoles of RC low pass filtering configured to attenuate the 470 kHzablation voltage. A high-impedance DC bias voltage provides anindication of when the (very low-resistance) thermocouple is notpresent.

Basic Power Control Scheme

Referring now to FIG. 15, one embodiment of energy delivery isillustrated in which dual, sequentially implemented algorithms areemployed to control power delivered. This method of energy delivery canbe applied independently to each RF output, or each RF channel (pair ofRF outputs). When an ablation catheter's electrodes are cool (e.g. atbody temperature) and thus far from a user-programmed target temperature(e.g. greater than 5° C. from a target ablation temperature) as measuredby the system's thermocouples or other temperature sensors, energydelivery may be generated at a fixed level of power, irrespective oftemperature sensed by the thermocouples or other temperature sensors(first algorithm). In one embodiment, a maximum level of power (e.g.P_(max)=16 watts) may be delivered. When the temperature reaches apredetermined temperature band (e.g., T<5° C. from the targettemperature), the system changes from fixed (e.g. maximum) power leveldelivery to energy delivery controlled to temperature (second algorithmwhere power delivery is regulated by a temperature control loop). Whenin the temperature control loop, the system changes the duty cycle (“on”time/“off” time ratio) to allow the tissue temperature to controllablyprogress to the desired target temperature, such as to minimize orprevent overshoot. In an alternative embodiment, the thresholdtemperature at which the second algorithm is implemented, is also set bythe user through, e.g., the user interface. In other words, in additionto the target temperature, a threshold temperature is also set by theuser, instead of a fixed amount such as the 5° C. mentioned above.

In one embodiment, the duty cycle (field) period is approximately 16-17msec, such that if 10 watts RMS power is to be delivered for a specificfield (entire length) and 100 watts RMS is delivered during the “on”period, the “on” period duration would be set to 1.7 msec and the “off”period duration would be set to 15.3 msec. A typical duty cycle may beabout 10%, and a typical voltage applied may be about 100 volts RMS. Ifthe nominal load (impedance of the tissue) is about 100 ohms, this 10%duty cycle would yield 100 watts RMS for the 17 msec period. In anycase, a target temperature between 50° C.-70° C. (e.g., 60° C.) may beset, and the system may deliver energy to heat and ablate as describedin reference to FIG. 15.

Referring now to FIG. 16, a flow chart of another power controlalgorithm is illustrated. This method of energy delivery can be appliedindependently to each RF output, or each RF channel (pair of RFoutputs). The control method uses a main control loop and a secondarycontrol loop. The main loop controls the duty cycle and compares theactual power to a power goal. The proportional difference between thegoal and the actual power is added to an integration register. Thedifference between the last power delivered and the present power (thederivative) is subtracted from the integration register. The new valuein the integration register sets the duty cycle value.

The secondary control loop controls the power goal and compares theactual temperature (measured) to a temperature goal. The proportionaldifference between the goal and the actual temperature is added to anintegration register. The difference between the last temperaturemeasured and the present temperature (the derivative) is subtracted fromthe integration register. The value in the integration register sets thepower goal value. If the power goal value is greater than the powerlimit, the power goal is set to equal the power limit.

The algorithm of FIG. 16 provides a safe and efficient way of deliveringpower to create a lesion, and is particularly effective at limitingovershoot of achieved temperature (above the target temperature).

In the algorithm of FIG. 16, if the target temperature is reached priorto reaching a maximum power, the ablation may occur without everdelivering the maximum power. If the target temperature is not achieved,the system will limit power delivery to a maximum power. In oneembodiment, an algorithm applies a set of power limits specific to thebipolar-monopolar ratio used. For one or more ablation catheters of thepresent invention, this set of power limits is as listed in Table 1below:

TABLE 1 Bipolar-Monopolar Ratio Power Limits Monopolar-only 10 Watts RMS1:1 10 Watts RMS 2:1 10 Watts RMS 4:1  8 Watts RMS Bipolar-only  6 WattsRMS

Referring now to FIGS. 17A, 17B and 17C, an algorithm for setting theratio of bipolar to monopolar energy delivery is illustrated. Thebipolar to monopolar energy delivery ratio is varied by adjusting thenumber (ratio) of monopolar to bipolar fields. Held constant are theduty cycle (“on” time and “off” time lengths), the field length (17msec) and the bipolar delivery phase angle. In this embodiment, thephase angle is set to 90° such that bipolar energy is twice monopolarenergy delivery at the same applied voltage, as has been describedabove. Referring specifically to FIG. 17A, a 1:1 ratio of bipolar tomonopolar energy delivery is achieved with a 1:2 ratio of bipolar tomonopolar fields (e.g. a set of two monopolar fields followed by onebipolar field, which repeat). Referring specifically to FIG. 17B, a 2:1ratio of bipolar to monopolar energy delivery is achieved with a 1:1ratio of bipolar to monopolar fields (e.g. a set of one monopolar fieldfollowed by one bipolar field, which repeat). Referring specifically toFIG. 17C, a 4:1 ratio of bipolar to monopolar energy delivery isachieved with a 2:1 ratio of bipolar to monopolar fields (e.g. a set ofone monopolar field followed by two bipolar fields, which repeat). In analternative embodiment, the bipolar to monopolar ratio is furtheradjusted by varying one or more of duty cycle, field length and phaseangle. In another alternative embodiment, one or more bipolar fields arereplaced with combo fields.

Referring now to FIGS. 18A 18B, another algorithm for setting the ratioof bipolar to monopolar energy delivery is illustrated. The bipolar tomonopolar energy delivery ratio is varied by adjusting duty cycle (“on”time and “off” time lengths). Held constant are the ratio of bipolar tomonopolar fields (set to 1:1), the field length (17 msec) and thebipolar delivery phase angle. In this embodiment, the phase angle isalso set to 90° such that bipolar energy is twice monopolar energydelivery at the same applied voltage, as has been described above.Referring specifically to FIG. 18A, a 2:1 ratio of bipolar to monopolarenergy delivery is achieved with a 1:1 ratio of bipolar to monopolar“on” times. In both the bipolar and monopolar fields, the duty cycle isset to 50%, or 8.5 msec of the 17 msec period. Referring specifically toFIG. 18B, a 4:1 ratio of bipolar to monopolar energy delivery isachieved with a 2:1 ratio of bipolar to monopolar “on” times. In boththe bipolar field, the “on” time is 10 msec (approx 58% duty cycle) andin the monopolar field the “on” time is 5 msec (approx 29% duty cycle).In an alternative embodiment, the bipolar to monopolar ratio is furtheradjusted by varying one or more of the ratio of bipolar to monopolarfields, field length and phase angle. In another alternative embodiment,one or more bipolar fields are replaced with combo fields.

Referring now to FIG. 19, another algorithm for setting the ratio ofbipolar to monopolar energy delivery is illustrated. The bipolar tomonopolar energy delivery ratio is varied by adjusting field length.Held constant are the ratio of bipolar to monopolar fields (set to 1:1),the duty cycle (within the fields—e.g. 10%) and the bipolar deliveryphase angle. In this embodiment, the phase angle is also set to 90° suchthat bipolar energy is twice monopolar energy delivery at the sameapplied voltage, as has been described above. A 4:1 ratio of bipolar tomonopolar energy delivery is achieved with a 2:1 ratio of bipolar tomonopolar field lengths (e.g. 34 msec to 17 msec respectively). In analternative embodiment, the bipolar to monopolar ratio is furtheradjusted by varying one or more of the ratio of bipolar to monopolarfields, field length and phase angle. In another alternative embodiment,one or more bipolar fields are replaced with combo fields.

In the embodiments of FIGS. 17A-C, 18A-B and 19, the applied voltage isalso held constant. In alternative embodiments, the voltage is varied tomodify the ratio of bipolar to monopolar power delivered. In theembodiments of FIGS. 17A-C, 18A-B and 19, some fields include thedelivery of bipolar energy. In alternative embodiments, these bipolarenergy delivery fields are replaced with combo energy delivery, and theassociated variables mathematically adjusted to achieve the desiredbipolar to monopolar ratio.

Referring now to FIG. 20, a schematic of an embodiment for interfacingRF outputs with an EKG diagnostic device is illustrated. It is importantthat the RF energy delivered is “isolated” from an EKG diagnostic deviceor module (such as a separate EKG monitor or an EKG monitor integratedinto the RF generator of the present invention). A resistor, such as a10 Kohm resistor in series with the output, can be used to attenuate theRF power yet let the mapping information pass through. The issue withsuch a configuration is the mapping information is also attenuateddramatically. In the embodiment of FIG. 20, a 1000 milliHenry inductorL1, is placed between the RF output 31 a and the input to the EKG moduleEKG1. The inductor provides sufficient attenuation of the high frequencyRF signal (e.g. 3300 ohms of impedance with RF delivered at 470 kHz ashas been described above), yet very low impedance in the lower frequencyspectrum representing EKG information. A second inductor L2, is placedbetween second RF output 31 b and a second input to the EKG module EKG2.A capacitor C1 is placed between EKG1 and EKG2, completing a low-passfilter which reduces the RF voltage that is “exposed” to an attached EKGdiagnostic device. Inductors can be placed between each RF output (i.e.connected to each electrode of an ablation catheter) and an associatedEKG diagnostic device input.

Referring now to FIG. 21, an embodiment of a remote control for the RFgenerator is illustrated. Remote control 500 is configured to sendcommands to an RFG of the present invention, via information input intouser interface 520 by an operator of the system. User interface 520 isconfigured to allow an operator to input system parameter and outputconfiguration information including but not limited to: electrodeselection; power delivery settings, targets and other power deliveryparameters; and other information. User interface 520 may be furtherconfigured to provide information to the operator, such as visual andaudible information including but not limited to: electrode selection,power delivery parameters and other information.

In one embodiment, remote control 500 provides full control of the RFGof the present invention, such that no other user interface is requiredto perform any and all functions of the RFG. In an alternativeembodiment, remote control 500 provides partial control of the RFG. Userinterface 520 may replace a user interface integral to an RFG, or workin combination with it. In one embodiment, user interface 520 is themaster control, overriding conflicting commands from a user interface ofthe RFG. In another embodiment, the user interface of the RFG is themaster control. User interface 520 includes a bank of switches, such asa membrane keypad, and/or other user input components, to enter commandsto be received by the RFG. User interface 520 further includes useroutput components such as indicator lights, displays such as LCDdisplays, and other means of presenting information to an operator ofthe RFG. In one embodiment, user interface 520 includes a touch screendisplay configured to provide information to the user and receivecommands from the user.

Remote control 500 includes a housing 501, such as a plastic housingwhich surrounds one or more electronic modules and includes userinterface 520 on its top, outer surface. In one embodiment, a bundle ofwires connect remote control 500 to the RFG of the present invention,such as via a ten pin receptacle integral to the housing of the RFG. Inan alternative embodiment, remote control 500 includes a wirelesstransceiver, not shown but possibly configured to send and receivewireless transfer of information to and from the RFG, such as via ahandshaking protocol which assures accuracy of information transfer.

Remote control 500 may be provided sterilized and/or may be covered witha disposable sterile bag, not shown, but configured to surround remotecontrol 500 and at least a portion of any wires attached to remotecontrol 500. The sterile assembly may be brought into the sterile fieldof a patient undergoing a sterile procedure, such as a cardiac ablationprocedure to treat atrial fibrillation, or a tumor ablation procedure.

The systems of the present invention may include one or more powerlimits which can be integrated into software and/or hardware of the RFG.The system may employ different power limits for different ablationcatheters. Alternatively or additionally, the system may employdifferent power limits for different bipolar-monopolar ratios. In oneembodiment, the system includes power limits from Table 1 above. In oneembodiment, different power limits (or sets of power limits as shown inthe above table) are used for different ablation catheters.Alternatively or additionally, power limits of 20-30 Watts RMS may beused by one or more algorithms for one or more ablation catheters of thepresent invention. In general, ablation catheters with larger electrodesmay correlate to a higher power limit than an ablation catheter withsmaller electrodes. The power limits are employed to limit clinicianerror as well as otherwise improve safety, such as by reducing thelikelihood of coagulum creation or ablation of untargeted tissue. It hasbeen demonstrated that in the instance where one or more electrodes haslimited or otherwise inadequate tissue contact, such as when a “hotspot”in the tissue may have been caused, the above power limits weresuccessful in avoiding the creation of coagulum.

The system of the present invention may include a limit on the minimumtime ablation energy is delivered. In one embodiment, a minimum energydelivery time is approximately 25 seconds. In another embodiment, aminimum energy delivery time is approximately 40 seconds.

The system of the present invention may include various means ofadjusting power levels (delivered) as well as the simultaneous ratio ofbipolar to monopolar power delivered. In one embodiment, time divisionmultiplexing (TDM) is utilized to set a power level and/or a bipolar tomonopolar ratio.

The system of the present invention may include one or more algorithmswhich adjust power delivery based on which form of ablation catheters isattached. The power delivery may be adjusted based one or moreparameters of the attached ablation catheter, such parameters includingbut not limited to: distance between two electrodes receiving energy;electrode geometry; thermocouple location; and combinations thereof.

It should be understood that numerous other configurations of thesystems, devices and methods described herein can be employed withoutdeparting from the spirit or scope of this application. It should beunderstood that the system includes multiple functional components, suchas the RF generator and various ablation catheters of the presentinvention. In one embodiment, the ablation catheter consists of acatheter shaft, a carrier assembly for providing electrodes in aresiliently biased configuration, a control shaft for deploying andwithdrawing the carrier assembly, and a coupler for attaching thecontrol shaft to the carrier assembly. The carrier assembly is a supportstructure which is shiftable from a storage or confined configuration,such as a radially constrained configuration, to a deployed or expandedconfiguration. The carrier assembly can include wires, ribbons, cablesand struts, made of metals, non-metals or combinations of both. Thecarrier assembly can be constructed of one or more materials, includingboth metals and non-metals. Typical metals chosen for carrier assemblyconstruction include but are not limited to: stainless steel, Nitinol,Elgiloy™, other alloys and combinations thereof.

The ablation catheters of the present invention may include a steerableouter sheath, or may work in conjunction as a system with a separatesteerable outer sheath. One or more tubular components of the ablationcatheter may be steerable such as with the inclusion of a controllablepull wire at or near the distal end. The ablation catheters of thepresent invention may be inserted over the wire, such as via a lumenwithin one of the tubular conduits such as within a lumen of the tubularbody member or control shaft, or alternatively the catheter may includea rapid exchange sidecar at or near its distal end, consisting of asmall projection with a guidewire lumen therethrough. A guidewire lumenmay be included solely for the guidewire, or may provide other functionssuch as a vacuum lumen for an integral suction port integrated at thedistal portion of the carrier assembly.

The ablation catheters of the present invention further include one ormore ablation elements. In some embodiments, one or more ablationelements are electrodes configured to deliver RF energy. Other forms ofenergy, alternative or in addition to RF, may be delivered, includingbut not limited to: acoustic energy and ultrasound energy;electromagnetic energy such as electrical, magnetic, microwave andradiofrequency energies; thermal energy such as heat and cryogenicenergies; chemical energy; light energy such as infrared and visiblelight energies; mechanical energy; radiation; and combinations thereof.The RF generator of the present invention may further provide one of theadditional energy forms described immediately hereabove, in addition tothe RF energy.

One or more ablation elements may comprise a drug delivery pump or adevice to cause mechanical tissue damage such as a forwardly advanceablespike or needle. The ablation elements can deliver energy individually,in combination with or in serial fashion with other ablation elements.The ablation elements can be electrically connected in parallel, inseries, individually, or combinations thereof. The ablation catheter mayinclude cooling means, such as fins or other heat sinking geometries, toprevent undesired tissue damage and/or blood clotting. The ablationelements may be constructed of various materials, such as plates ofmetal and coils of wire for RF energy delivery. The electrodes can takeon various shapes including shapes used to focus energy such as a hornshape to focus sound energy, and shapes to assist in cooling such as ageometry providing large surface area. Electrodes can vary within asingle carrier assembly, such as a spiral array of electrodes or anumbrella tip configuration wherein electrodes farthest from the centralaxis of the catheter have the largest major axis. Wires and otherflexible conduits are attached to the ablation elements, such aselectrical energy carrying wires for RF electrodes or ultrasoundcrystals, and tubes for cryogenic delivery.

The ablation catheter of the present invention may include a handleactivating or otherwise controlling one or more functions of theablation catheter. The handle may also include various knobs or levers,such as rotating or sliding knobs which are operably connected toadvanceable conduits, or are operably connected to gear trains or camswhich are connected to advanceable conduits. These controls, such asknobs use to deflect a distal portion of a conduit, or to advance orretract the carrier assembly, may include a reversible locking mechanismsuch that a particular tip deflection or deployment amount can bemaintained through various manipulations of the system.

The ablation catheter may include one or more sensors, such as sensorsused to detect chemical activity; light; electrical activity; pH;temperature; pressure; fluid flow or another physiologic parameter.These sensors can be used to map electrical activity, measuretemperature, or gather other information that may be used to modify theablation procedure. In one embodiment, one or more sensors, such as amapping electrode, can also be used to ablate tissue.

Numerous components internal to the patient, such as the carrierassembly or electrodes, may include one or more visual markers such asradiopaque markers visible under fluoroscopy, or ultrasound markers.

Selection of the tissue to be ablated may be based on a diagnosis ofaberrant conduit or conduits, or based on anatomical location. RF energymay be delivered first, followed by another energy type in the samelocation, such as when a single electrode can deliver more than one typeof energy, such as RF and ultrasound energy. Alternatively oradditionally, a first procedure may be performed utilizing one type ofenergy, followed by a second procedure utilizing a different form ofenergy. The second procedure may be performed shortly after the firstprocedure, such as within four hours, or at a later date such as greaterthan twenty-four hours after the first procedure. Numerous types oftissue can be ablated utilizing the devices, systems and methods of thepresent invention. For example, the various aspects of the inventionhave application in procedures for ablating tissue in the prostrate,brain, gall bladder, uterus, other organs and regions of the body, and atumor, such as regions with an accessible wall or flat tissue surface.In some embodiments, heart tissue is ablated, such as left atrialtissue.

In another embodiment of the system of the present invention, anablation catheter and a heat sensing technology are included. The heatsensing technology, includes sensor means that may be placed on thechest of the patient, the esophagus or another area in close enoughproximity to the tissue being ablated to directly measure temperatureeffects of the ablation, such as via a temperature sensor, or indirectlysuch as through the use of an infrared camera. In these embodiments, theRFG includes means of receiving the temperature information from theheat sensing technology, similar to the handling of the temperatureinformation from thermocouples of the ablation catheters. Thisadditional temperature information can be used in one or more algorithmsfor power delivery, as has been described above, and particularly as asafety threshold which shuts off or otherwise decreased power delivery.A temperature threshold will depend on the location of the heat sensingtechnology sensor means, as well as where the ablation energy is beingdelivered. The threshold may be adjustable, and may be automaticallyconfigured.

Numerous kit configurations are also to be considered within the scopeof this application. An ablation catheter is provided with multiplecarrier assemblies. These carrier assemblies can be removed for thetubular body member of the catheter, or may include multiple tubularbody members in the kit. The multiple carrier assemblies can havedifferent patterns, different types or amounts of electrodes, and havenumerous other configurations including compatibility with differentforms of energy.

Though the ablation device has been described in terms of an endocardialand transcutaneous method of use, the array may be used on the heartduring open heart surgery, open chest surgery, or minimally invasivethoracic surgery. Thus, during open chest surgery, a short catheter orcannula carrying the carrier assembly and its electrodes may be insertedinto the heart, such as through the left atrial appendage or an incisionin the atrium wall, to apply the electrodes to the tissue to be ablated.Also, the carrier assembly and its electrodes may be applied to theepicardial surface of the atrium or other areas of the heart to detectand/or ablate arrhythmogenic foci from outside the heart.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims. In addition,where this application has listed the steps of a method or procedure ina specific order, it may be possible, or even expedient in certaincircumstances, to change the order in which some steps are performed,and it is intended that the particular steps of the method or procedureclaim set forth herebelow not be construed as being order-specificunless such order specificity is expressly stated in the claim.

1. A radio frequency tissue ablation system comprising a radio frequencygenerator, the generator comprising a radio frequency source, at leastfour independently controllable radio frequency outputs, a userinterface and a controller configured to delivery radio frequency energyfrom the radio frequency source to the radio frequency outputs in one ofat least two different output configurations in response to aconfiguration selection made through the user interface.
 2. The systemof claim 1 wherein the controller is further configured to operate eachoutput in either a monopolar mode or in a bipolar mode.
 3. The system ofclaim 2 further comprising a ground pad, the ground pad being connectedto a ground source when the outputs are operated in both monopolar modeand bipolar mode.
 4. The system of claim 2 wherein the controller isfurther configured to operate each output in a combinationmonopolar/bipolar mode.
 5. The system of claim 1 wherein the controlleris further configured to selectively connect different pairs of theradio frequency outputs in a bipolar mode in response to a configurationselection made through the user interface.
 6. The system of claim 1wherein the controller is further configured to deliver radio frequencyenergy from the radio frequency source to the radio frequency outputs ina plurality of successive time fields each having a period.
 7. Thesystem of claim 6 wherein the time fields have a duty cycle comprising aportion of the period when radio frequency energy is being delivered tothe outputs and another portion of the period when radio frequencyenergy is not being delivered to the outputs.
 8. The system of claim 7wherein the controller is further configured to adjust the duty cycle inresponse to a configuration selection made through the user interface.9. The system of claim 6 wherein at least one time field of theplurality of the successive time fields is monopolar for at least aportion of the period, and at least another time field of the successivetime fields is bipolar for at least a portion of the period.
 10. Thesystem of claim 9 wherein the controller is configured to adjust a ratioof bipolar to monopolar time fields in response to a configurationselection made through the user interface.
 11. The system of claim 9wherein at least one time field is a combination monopolar/bipolar timefield.
 12. The system of claim 6 wherein the controller is furtherconfigured to adjust a length of at least one time field in response toa configuration selection made through the user interface.
 13. Thesystem of claim 1 wherein the radio frequency source is a constantvoltage source.
 14. The system of claim 1 wherein the radio frequencysource is a variable voltage source.
 15. The system of claim 14 whereinthe controller is further configured to vary voltage amplitude inresponse to a configuration selection made through the user interface.16. The system of claim 1 wherein the controller is further configuredto adjust voltage phase angle of the RF source.
 17. The system of claim16 wherein the controller is further configured to adjust voltage phaseangle of the radio frequency source in response to a configurationselection made through the user interface.
 18. The system of claim 1wherein the controller comprises a time division multiplexor.
 19. Thesystem of claim 1 wherein the radio frequency generator furthercomprises an electrode tool interface configured to detect an identifierof a radio frequency electrode tool connected to the interface, thecontroller being configured to adjust radio frequency energy deliveryparameters to an radio frequency electrode tool based on the identifierdetected by the interface.
 20. The system of claim 19 further comprisinga first radio frequency electrode tool having a first electrodeconfiguration and second radio frequency electrode tool having a secondelectrode configuration different from the first electrodeconfiguration, the first and second radio frequency electrode tools eachcomprising a connector adapted to connect to the radio frequencygenerator electrode tool interface, the connector of each toolcomprising a unique identifier adapted to communicate with the radiofrequency generator electrode tool interface.
 21. The system of claim 1further comprising a ground pad, the controller being configured toconnect and disconnect the ground pad to a ground source in response toa configuration selection made through the user interface.
 22. Thesystem of claim 1 wherein each output comprises an output line, a returnline and a resistance between output line and the return line.
 23. Thesystem of claim 22 wherein the resistance has a value that providessignal stability on the output during light load conditions at theoutput.
 24. A radio frequency ablation system comprising: a radiofrequency generator; a plurality of radio frequency electrodes; atemperature sensor; and a controller communicating with the temperaturesensor to control an amount of energy delivered to the electrodes in afirst portion of an energy delivery session irrespective of temperaturesensed by the temperature sensor and in a second portion of the energydelivery session based on the temperature sensed by the temperaturesensor.
 25. The system of claim 24 wherein the controller is configuredto cease energy delivery to the electrodes when a predetermined targettemperature is sensed by the temperature sensor.
 26. The system of claim25 further comprising a user interface adapted to set the targettemperature.
 27. The system of claim 25 wherein the controller isfurther configured to cease the first portion of the energy deliverysession when the temperature sensor reaches a threshold temperature thatis a predetermined amount lower than the target temperature.
 28. Thesystem of claim 24 wherein the controller is configured to cease thefirst portion of the energy delivery session when temperature sensed bythe temperature sensor reaches a threshold temperature.
 29. The systemof claim 28 further comprising a user interface adapted to set thethreshold temperature.
 30. The system of claim 24 wherein the controlleris configured to independently control energy delivery to eachelectrode.
 31. The system of claim 30 further comprising a temperaturesensor associated with each electrode, the controller independentlycommunicating with each temperature sensor in the delivering step tocontrol the amount of energy delivered to the electrodes.
 32. The systemof claim 24 wherein the controller is configured to independentlycontrol energy to a pair of electrodes and at least one other electrode.33. The system of claim 24 wherein the controller is configured todeliver radio frequency energy in a plurality of successive time fieldseach having a period and a duty cycle comprising a portion of the periodwhen radio frequency energy is being delivered to the electrodes andanother portion of the period when radio frequency energy is not beingdelivered to the electrodes.
 34. The system of claim 33 wherein thecontroller is further configured to adjust the duty cycle based onmonitored temperature.
 35. The system of claim 24 wherein the controlleris configured to compare temperature sensed by the temperature sensor toa target temperature and to adjust a power goal based on the comparison.36. The system of claim 35 wherein the controller is further configuredto compare the power goal to a power limit and to reset the power goalto the power limit if the power goal exceeds the power limit.
 37. Aradio frequency energy generation system for delivering radio frequencyenergy to a cardiac ablation catheter, comprising: a radio frequencygenerator adapted to deliver radio frequency energy in both monopolarand bipolar modes to an ablation catheter, wherein the ablation cathetercomprises an electrode array comprising at least one electrode; an EKGmonitoring unit adapted to monitor and map signals detected by theplurality of ablation catheters; and an interface unit comprising aninductor which couples the radio frequency generator and EKG monitoringunit to filter radio frequency signals from EKG signals received by theEKG monitoring unit.
 38. The system of claim 37 wherein the at least oneelectrode is adapted to monitor the temperature of atrial tissueadjacent the electrode, and wherein the generator generates radiofrequency energy based on the temperature of the atrial tissue.
 39. Thesystem of claim 38 wherein the at least one electrode comprises aplurality of electrodes, and wherein the generator is adapted toindependently monitor the temperature of atrial tissue measured by eachof the plurality of electrodes, and wherein the radio frequencygenerator is adapted to generate and deliver radio frequency energy toeach of the plurality of electrodes based on the independently monitoredtemperatures.
 40. The system of claim 37 wherein the EKG monitoring unitcomprises a plurality of inputs and an inductor associated with eachinput.
 41. The system of claim 37 wherein the generator is adapted todeliver energy in a bipolar mode, a monopolar mode, and a combination ofboth bipolar and monopolar modes.
 42. The system of claim 41 wherein thegenerator is adapted to deliver a combination of bipolar and monopolarradio frequency energy to the electrode array in bipolar to monopolarratios of at least 4:1, 2:1, and 1:1.
 43. A method of delivering radiofrequency ablation energy to a patient's tissue comprising deliveringradio frequency energy to a plurality of electrodes to heat thepatient's tissue in first and second portions of an energy deliverysession; monitoring temperature of the patient's tissue during thedelivering step; delivering radio frequency energy at a power level inthe first portion of the energy delivery session, the power level beingirrespective of monitored tissue temperature; and controlling radiofrequency energy delivered to the electrodes in the second portion ofthe energy delivery session based on monitored tissue temperature. 44.The method of claim 43 further comprising ceasing energy delivery when apredetermined target tissue temperature is reached.
 45. The method ofclaim 44 further comprising setting the target tissue temperature. 46.The method of claim 44 further comprising ceasing the first portion ofthe energy delivery session when monitored tissue temperature reaches athreshold tissue temperature that is a predetermined amount lower thanthe target tissue temperature.
 47. The method of claim 43 furthercomprising ceasing the first portion of the energy delivery session whena threshold tissue temperature is reached.
 48. The method of claim 47further comprising setting the threshold tissue temperature.
 49. Themethod of claim 43 wherein at least one of the controlling stepscomprises independently controlling energy delivery to each electrode.50. The method of claim 43 wherein at least one of the controlling stepscomprises independently controlling energy delivery to a pair ofelectrodes and to at least one other electrode.
 51. The method of claim43 wherein the delivering step comprises delivering radio frequencyenergy in a plurality of successive time fields each having a period anda duty cycle comprising a portion of the period when radio frequencyenergy is being delivered to the electrodes and another portion of theperiod when radio frequency energy is not being delivered to theelectrodes.
 52. The method of claim 51 wherein at least one of thecontrolling steps comprises adjusting the duty cycle.
 53. The method ofclaim 43 wherein the step of controlling radio frequency energydelivered to the electrodes in the second portion of the energy deliverysession comprises comparing a monitored temperature to a targettemperature and adjusting a power goal.
 54. The method of claim 53wherein the delivering step comprises comparing the power goal to apower limit and resetting the power goal to the power limit if the powergoal exceeds the power limit.
 55. The method of claim 43 wherein thepatient's tissue comprises heart tissue, prostate tissue, brain tissue,gall bladder tissue, uterine tissue, or tumor tissue.